BASELINE: Update Chromium to 85.0.4183.14085-based

Change-Id: Iaa42f4680837c57725b1344f108c0196741f6057
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

19 files changed, 425 insertions, 61 deletions

diff --git a/chromium/fuchsia/base/BUILD.gn b/chromium/fuchsia/base/BUILD.gn
index 2dba9680aad..4e0d73dd164 100644
--- a/chromium/fuchsia/base/BUILD.gn
+++ b/chromium/fuchsia/base/BUILD.gn
@@ -4,30 +4,37 @@
 
 assert(is_fuchsia)
 
-import("//build/buildflag_header.gni")
 import("//build/config/fuchsia/generate_runner_scripts.gni")
-import("//fuchsia/release_channel.gni")
 import("//testing/test.gni")
 
 # Integration helpers for commonly used fuchsia.* APIs.
 source_set("base") {
   sources = [
     "config_reader.cc",
+    "feedback_registration.cc",
     "fuchsia_dir_scheme.cc",
     "init_logging.cc",
+    "inspect.cc",
     "mem_buffer_util.cc",
     "string_util.cc",
   ]
   public = [
     "config_reader.h",
+    "feedback_registration.h",
     "fuchsia_dir_scheme.h",
     "init_logging.h",
+    "inspect.h",
     "mem_buffer_util.h",
     "string_util.h",
   ]
   deps = [
     "//base",
+    "//components/version_info",
+    "//third_party/fuchsia-sdk/sdk/fidl/fuchsia.feedback",
     "//third_party/fuchsia-sdk/sdk/fidl/fuchsia.mem",
+    "//third_party/fuchsia-sdk/sdk/pkg/fdio",
+    "//third_party/fuchsia-sdk/sdk/pkg/sys_cpp",
+    "//third_party/fuchsia-sdk/sdk/pkg/sys_inspect_cpp",
     "//url",
   ]
 }
@@ -78,13 +85,6 @@ source_set("legacymetrics") {
   friend = [ ":*" ]
 }
 
-# Used to propagate release-qualified package names to integration test code.
-buildflag_header("release_channel_buildflags") {
-  header = "release_channel.h"
-  flags = [ "FUCHSIA_RELEASE_CHANNEL_SUFFIX=\"$release_channel_suffix\"" ]
-  visibility = [ "//fuchsia/*" ]
-}
-
 source_set("test_support") {
   testonly = true
   sources = [
@@ -106,7 +106,6 @@ source_set("test_support") {
   public_deps = [
     ":base",
     ":modular",
-    ":release_channel_buildflags",
     "//base",
     "//net",
     "//net:test_support",
@@ -120,6 +119,7 @@ source_set("test_support") {
 test("cr_fuchsia_base_unittests") {
   sources = [
     "agent_impl_unittests.cc",
+    "inspect_unittest.cc",
     "legacymetrics_client_unittest.cc",
     "legacymetrics_histogram_flattener_unittest.cc",
     "legacymetrics_user_event_recorder_unittest.cc",
@@ -132,6 +132,9 @@ test("cr_fuchsia_base_unittests") {
     "//base:testfidl",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
+    "//components/version_info",
     "//testing/gtest",
+    "//third_party/fuchsia-sdk/sdk/pkg/sys_cpp",
+    "//third_party/fuchsia-sdk/sdk/pkg/sys_inspect_cpp",
   ]
 }
diff --git a/chromium/fuchsia/base/DEPS b/chromium/fuchsia/base/DEPS
index 9455f2ca503..5ded5f1b3d8 100644
--- a/chromium/fuchsia/base/DEPS
+++ b/chromium/fuchsia/base/DEPS
@@ -1,4 +1,5 @@
 include_rules = [
+  "+components/version_info",
   "+mojo/public",
   "+third_party/blink/public/common/messaging",
   "+third_party/blink/public/mojom/messaging",
diff --git a/chromium/fuchsia/base/agent_impl.cc b/chromium/fuchsia/base/agent_impl.cc
index b692599f2a2..4ecd277425e 100644
--- a/chromium/fuchsia/base/agent_impl.cc
+++ b/chromium/fuchsia/base/agent_impl.cc
@@ -7,7 +7,6 @@
 #include <lib/sys/cpp/component_context.h>
 
 #include "base/bind.h"
-#include "base/fuchsia/default_context.h"
 
 namespace cr_fuchsia {
 
diff --git a/chromium/fuchsia/base/agent_impl.h b/chromium/fuchsia/base/agent_impl.h
index b630dc8bb6c..389efb30b28 100644
--- a/chromium/fuchsia/base/agent_impl.h
+++ b/chromium/fuchsia/base/agent_impl.h
@@ -15,7 +15,6 @@
 
 #include "base/bind.h"
 #include "base/containers/flat_map.h"
-#include "base/fuchsia/default_context.h"
 #include "base/fuchsia/scoped_service_binding.h"
 #include "base/fuchsia/service_provider_impl.h"
 #include "base/macros.h"
diff --git a/chromium/fuchsia/base/agent_manager.h b/chromium/fuchsia/base/agent_manager.h
index 7f60750e471..17fd60c254c 100644
--- a/chromium/fuchsia/base/agent_manager.h
+++ b/chromium/fuchsia/base/agent_manager.h
@@ -10,7 +10,6 @@
 #include <lib/sys/cpp/component_context.h>
 
 #include "base/containers/flat_map.h"
-#include "base/fuchsia/default_context.h"
 #include "base/macros.h"
 #include "base/strings/string_piece.h"
 
diff --git a/chromium/fuchsia/base/config_reader.cc b/chromium/fuchsia/base/config_reader.cc
index 87eaab8e48c..0c73357e93a 100644
--- a/chromium/fuchsia/base/config_reader.cc
+++ b/chromium/fuchsia/base/config_reader.cc
@@ -29,14 +29,14 @@ base::Optional<base::Value> ReadPackageConfig() {
     return base::nullopt;
   }
 
-  base::JSONReader reader;
-  base::Optional<base::Value> parsed = reader.Read(file_content);
-  CHECK(parsed) << "Failed to parse " << path.value() << ": "
-                << reader.GetErrorMessage();
-  CHECK(parsed->is_dict()) << "Config is not a JSON dictinary: "
-                           << path.value();
-
-  return std::move(parsed.value());
+  base::JSONReader::ValueWithError parsed =
+      base::JSONReader::ReadAndReturnValueWithError(file_content);
+  CHECK(parsed.value) << "Failed to parse " << path.value() << ": "
+                      << parsed.error_message;
+  CHECK(parsed.value->is_dict())
+      << "Config is not a JSON dictionary: " << path.value();
+
+  return std::move(parsed.value);
 }
 
 }  // namespace
diff --git a/chromium/fuchsia/base/context_provider_test_connector.cc b/chromium/fuchsia/base/context_provider_test_connector.cc
index ba5f1234432..307f0bd9d0f 100644
--- a/chromium/fuchsia/base/context_provider_test_connector.cc
+++ b/chromium/fuchsia/base/context_provider_test_connector.cc
@@ -12,10 +12,8 @@
 #include <zircon/processargs.h>
 #include <utility>
 
-#include "base/fuchsia/default_context.h"
 #include "base/fuchsia/fuchsia_logging.h"
-#include "base/strings/strcat.h"
-#include "fuchsia/base/release_channel.h"
+#include "base/fuchsia/process_context.h"
 
 namespace cr_fuchsia {
 
@@ -24,9 +22,8 @@ fidl::InterfaceHandle<fuchsia::io::Directory> StartWebEngineForTests(
         component_controller_request,
     const base::CommandLine& command_line) {
   fuchsia::sys::LaunchInfo launch_info;
-  launch_info.url = base::StrCat({"fuchsia-pkg://fuchsia.com/web_engine",
-                                  BUILDFLAG(FUCHSIA_RELEASE_CHANNEL_SUFFIX),
-                                  "#meta/context_provider.cmx"});
+  launch_info.url =
+      "fuchsia-pkg://fuchsia.com/web_engine#meta/context_provider.cmx";
   launch_info.arguments = command_line.argv();
 
   // Clone stderr from the current process to WebEngine and ask it to
@@ -43,8 +40,7 @@ fidl::InterfaceHandle<fuchsia::io::Directory> StartWebEngineForTests(
       web_engine_services_dir.NewRequest().TakeChannel();
 
   fuchsia::sys::LauncherPtr launcher;
-  base::fuchsia::ComponentContextForCurrentProcess()->svc()->Connect(
-      launcher.NewRequest());
+  base::ComponentContextForProcess()->svc()->Connect(launcher.NewRequest());
   launcher->CreateComponent(std::move(launch_info),
                             std::move(component_controller_request));
 
diff --git a/chromium/fuchsia/base/context_provider_test_connector.h b/chromium/fuchsia/base/context_provider_test_connector.h
index 0d5ca1fd707..5c4604b25bc 100644
--- a/chromium/fuchsia/base/context_provider_test_connector.h
+++ b/chromium/fuchsia/base/context_provider_test_connector.h
@@ -20,7 +20,6 @@ fidl::InterfaceHandle<fuchsia::io::Directory> StartWebEngineForTests(
     const base::CommandLine& command_line =
         base::CommandLine(base::CommandLine::NO_PROGRAM));
 
-// TODO(crbug.com/1046615): Use test manifests for package specification.
 fuchsia::web::ContextProviderPtr ConnectContextProvider(
     fidl::InterfaceRequest<fuchsia::sys::ComponentController>
         component_controller_request,
diff --git a/chromium/fuchsia/base/feedback_registration.cc b/chromium/fuchsia/base/feedback_registration.cc
new file mode 100644
index 00000000000..d8bee5ff647
--- /dev/null
+++ b/chromium/fuchsia/base/feedback_registration.cc
@@ -0,0 +1,30 @@
+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "fuchsia/base/feedback_registration.h"
+
+#include <fuchsia/feedback/cpp/fidl.h>
+#include <lib/sys/cpp/component_context.h>
+
+#include "base/fuchsia/process_context.h"
+#include "base/strings/string_piece.h"
+#include "components/version_info/version_info.h"
+
+namespace cr_fuchsia {
+
+void RegisterCrashReportingFields(base::StringPiece component_url,
+                                  base::StringPiece crash_product_name) {
+  fuchsia::feedback::CrashReportingProduct product_data;
+  product_data.set_name(crash_product_name.as_string());
+  product_data.set_version(version_info::GetVersionNumber());
+  // TODO(https://crbug.com/1077428): Use the actual channel when appropriate.
+  // For now, always set it to the empty string to avoid reporting "missing".
+  product_data.set_channel("");
+  base::ComponentContextForProcess()
+      ->svc()
+      ->Connect<fuchsia::feedback::CrashReportingProductRegister>()
+      ->Upsert(component_url.as_string(), std::move(product_data));
+}
+
+}  // namespace cr_fuchsia
diff --git a/chromium/fuchsia/base/feedback_registration.h b/chromium/fuchsia/base/feedback_registration.h
new file mode 100644
index 00000000000..7e983bf6a70
--- /dev/null
+++ b/chromium/fuchsia/base/feedback_registration.h
@@ -0,0 +1,22 @@
+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FUCHSIA_BASE_FEEDBACK_REGISTRATION_H_
+#define FUCHSIA_BASE_FEEDBACK_REGISTRATION_H_
+
+#include "base/strings/string_piece_forward.h"
+
+namespace cr_fuchsia {
+
+// Overrides the default Fuchsia product info in crash reports.
+// Crashes for the component |component_url| will contain |crash_product_name|,
+// the version from version_info, and an appropriate value for the release
+// channel. |component_url| must match the current component. The calling
+// process must have access to "fuchsia.feedback.CrashReportingProductRegister".
+void RegisterCrashReportingFields(base::StringPiece component_url,
+                                  base::StringPiece crash_product_name);
+
+}  // namespace cr_fuchsia
+
+#endif  // FUCHSIA_BASE_FEEDBACK_REGISTRATION_H_
\ No newline at end of file
diff --git a/chromium/fuchsia/base/frame_test_util.cc b/chromium/fuchsia/base/frame_test_util.cc
index c234b3a97fd..2150cd86360 100644
--- a/chromium/fuchsia/base/frame_test_util.cc
+++ b/chromium/fuchsia/base/frame_test_util.cc
@@ -54,4 +54,19 @@ fuchsia::web::LoadUrlParams CreateLoadUrlParamsWithUserActivation() {
   return load_url_params;
 }
 
+fuchsia::web::WebMessage CreateWebMessageWithMessagePortRequest(
+    fidl::InterfaceRequest<fuchsia::web::MessagePort> message_port_request,
+    fuchsia::mem::Buffer buffer) {
+  fuchsia::web::OutgoingTransferable outgoing;
+  outgoing.set_message_port(std::move(message_port_request));
+
+  std::vector<fuchsia::web::OutgoingTransferable> outgoing_vector;
+  outgoing_vector.push_back(std::move(outgoing));
+
+  fuchsia::web::WebMessage web_message;
+  web_message.set_outgoing_transfer(std::move(outgoing_vector));
+  web_message.set_data(std::move(buffer));
+  return web_message;
+}
+
 }  // namespace cr_fuchsia
diff --git a/chromium/fuchsia/base/frame_test_util.h b/chromium/fuchsia/base/frame_test_util.h
index 2c2ee036456..20534eaf5e9 100644
--- a/chromium/fuchsia/base/frame_test_util.h
+++ b/chromium/fuchsia/base/frame_test_util.h
@@ -31,6 +31,12 @@ base::Optional<base::Value> ExecuteJavaScript(fuchsia::web::Frame* frame,
 // autoplay to be used, which is used by many media tests.
 fuchsia::web::LoadUrlParams CreateLoadUrlParamsWithUserActivation();
 
+// Creates a WebMessage with one outgoing transferable set to
+// |message_port_request| and data set to |buffer|.
+fuchsia::web::WebMessage CreateWebMessageWithMessagePortRequest(
+    fidl::InterfaceRequest<fuchsia::web::MessagePort> message_port_request,
+    fuchsia::mem::Buffer buffer);
+
 }  // namespace cr_fuchsia
 
 #endif  // FUCHSIA_BASE_FRAME_TEST_UTIL_H_
diff --git a/chromium/fuchsia/base/inspect.cc b/chromium/fuchsia/base/inspect.cc
new file mode 100644
index 00000000000..775ae986618
--- /dev/null
+++ b/chromium/fuchsia/base/inspect.cc
@@ -0,0 +1,28 @@
+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "fuchsia/base/inspect.h"
+
+#include <lib/sys/inspect/cpp/component.h>
+
+#include "components/version_info/version_info.h"
+
+namespace cr_fuchsia {
+
+namespace {
+const char kVersion[] = "version";
+const char kLastChange[] = "last_change_revision";
+}  // namespace
+
+void PublishVersionInfoToInspect(sys::ComponentInspector* inspector) {
+  // These values are managed by the inspector, since they won't be updated over
+  // the lifetime of the component.
+  // TODO(https://crbug.com/1077428): Add release channel.
+  inspector->root().CreateString(kVersion, version_info::GetVersionNumber(),
+                                 inspector);
+  inspector->root().CreateString(kLastChange, version_info::GetLastChange(),
+                                 inspector);
+}
+
+}  // namespace cr_fuchsia
diff --git a/chromium/fuchsia/base/inspect.h b/chromium/fuchsia/base/inspect.h
new file mode 100644
index 00000000000..4d8d35335ee
--- /dev/null
+++ b/chromium/fuchsia/base/inspect.h
@@ -0,0 +1,20 @@
+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef FUCHSIA_BASE_INSPECT_H_
+#define FUCHSIA_BASE_INSPECT_H_
+
+namespace sys {
+class ComponentInspector;
+}  // namespace sys
+
+namespace cr_fuchsia {
+
+// Publish the Chromium version via the Inspect API. The lifetime of
+// |inspector| has to be the same as the component it belongs to.
+void PublishVersionInfoToInspect(sys::ComponentInspector* inspector);
+
+}  // namespace cr_fuchsia
+
+#endif  // FUCHSIA_BASE_INSPECT_H_
\ No newline at end of file
diff --git a/chromium/fuchsia/base/inspect_unittest.cc b/chromium/fuchsia/base/inspect_unittest.cc
new file mode 100644
index 00000000000..7a2bff50c81
--- /dev/null
+++ b/chromium/fuchsia/base/inspect_unittest.cc
@@ -0,0 +1,95 @@
+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "fuchsia/base/inspect.h"
+
+#include <lib/fdio/directory.h>
+#include <lib/inspect/cpp/hierarchy.h>
+#include <lib/inspect/cpp/reader.h>
+#include <lib/inspect/service/cpp/reader.h>
+#include <lib/sys/cpp/component_context.h>
+#include <lib/sys/inspect/cpp/component.h>
+#include <cstdint>
+#include <memory>
+
+#include "base/task/single_thread_task_executor.h"
+#include "base/test/task_environment.h"
+#include "components/version_info/version_info.h"
+#include "fuchsia/base/mem_buffer_util.h"
+#include "fuchsia/base/string_util.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace cr_fuchsia {
+
+namespace {
+
+const char kVersion[] = "version";
+const char kLastChange[] = "last_change_revision";
+
+class InspectTest : public ::testing::Test {
+ public:
+  InspectTest() {
+    fidl::InterfaceHandle<fuchsia::io::Directory> incoming_directory;
+    auto incoming_services =
+        std::make_shared<sys::ServiceDirectory>(std::move(incoming_directory));
+    context_ = std::make_unique<sys::ComponentContext>(
+        std::move(incoming_services),
+        published_root_directory_.NewRequest().TakeChannel());
+    inspector_ = std::make_unique<sys::ComponentInspector>(context_.get());
+    base::RunLoop().RunUntilIdle();
+  }
+
+  InspectTest(const InspectTest&) = delete;
+  InspectTest& operator=(const InspectTest&) = delete;
+
+ protected:
+  base::test::SingleThreadTaskEnvironment task_environment_{
+      base::test::SingleThreadTaskEnvironment::MainThreadType::IO};
+  std::unique_ptr<sys::ComponentContext> context_;
+  fidl::InterfaceHandle<fuchsia::io::Directory> published_root_directory_;
+  std::unique_ptr<sys::ComponentInspector> inspector_;
+};
+
+}  // namespace
+
+TEST_F(InspectTest, PublishVersionInfoToInspect) {
+  cr_fuchsia::PublishVersionInfoToInspect(inspector_.get());
+  fidl::InterfaceHandle<fuchsia::io::Directory> directory;
+  zx_status_t status = fdio_service_connect_at(
+      published_root_directory_.channel().get(), "diagnostics",
+      directory.NewRequest().TakeChannel().release());
+  ASSERT_EQ(ZX_OK, status);
+  std::unique_ptr<sys::ServiceDirectory> diagnostics =
+      std::make_unique<sys::ServiceDirectory>(std::move(directory));
+
+  // Access the inspect::Tree where the data is served. |tree| is in the
+  // directory created for the test, not the diagnostics directory for the test
+  // component.
+  fuchsia::inspect::TreePtr tree;
+  diagnostics->Connect(tree.NewRequest());
+  fuchsia::inspect::TreeContent content;
+  base::RunLoop run_loop;
+  tree->GetContent([&content, &run_loop](fuchsia::inspect::TreeContent c) {
+    content = std::move(c);
+    run_loop.Quit();
+  });
+  run_loop.Run();
+
+  // Parse the data as an inspect::Hierarchy.
+  ASSERT_TRUE(content.has_buffer());
+  std::string buffer_data;
+  cr_fuchsia::StringFromMemBuffer(content.buffer(), &buffer_data);
+  inspect::Hierarchy hierarchy =
+      inspect::ReadFromBuffer(cr_fuchsia::StringToBytes(buffer_data))
+          .take_value();
+
+  auto* property =
+      hierarchy.node().get_property<inspect::StringPropertyValue>(kVersion);
+  EXPECT_EQ(property->value(), version_info::GetVersionNumber());
+  property =
+      hierarchy.node().get_property<inspect::StringPropertyValue>(kLastChange);
+  EXPECT_EQ(property->value(), version_info::GetLastChange());
+}
+
+}  // namespace cr_fuchsia
diff --git a/chromium/fuchsia/base/legacymetrics_client.cc b/chromium/fuchsia/base/legacymetrics_client.cc
index a2d45a83ac8..58f384124c1 100644
--- a/chromium/fuchsia/base/legacymetrics_client.cc
+++ b/chromium/fuchsia/base/legacymetrics_client.cc
@@ -11,8 +11,8 @@
 #include <utility>
 #include <vector>
 
-#include "base/fuchsia/default_context.h"
 #include "base/fuchsia/fuchsia_logging.h"
+#include "base/fuchsia/process_context.h"
 #include "base/logging.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
@@ -34,11 +34,13 @@ void LegacyMetricsClient::Start(base::TimeDelta report_interval) {
   DCHECK(!metrics_recorder_) << "Start() called more than once.";
 
   report_interval_ = report_interval;
-  metrics_recorder_ = base::fuchsia::ComponentContextForCurrentProcess()
+  metrics_recorder_ = base::ComponentContextForProcess()
                           ->svc()
                           ->Connect<fuchsia::legacymetrics::MetricsRecorder>();
   metrics_recorder_.set_error_handler(fit::bind_member(
       this, &LegacyMetricsClient::OnMetricsRecorderDisconnected));
+  metrics_recorder_.events().OnCloseSoon =
+      fit::bind_member(this, &LegacyMetricsClient::OnCloseSoon);
   user_events_recorder_ = std::make_unique<LegacyMetricsUserActionRecorder>();
   ScheduleNextReport();
 }
@@ -54,7 +56,18 @@ void LegacyMetricsClient::SetReportAdditionalMetricsCallback(
   report_additional_callback_ = std::move(callback);
 }
 
+void LegacyMetricsClient::SetNotifyFlushCallback(NotifyFlushCallback callback) {
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
+  DCHECK(callback);
+  DCHECK(!metrics_recorder_)
+      << "SetNotifyFlushCallback() must be called before Start().";
+
+  notify_flush_callback_ = std::move(callback);
+}
+
 void LegacyMetricsClient::ScheduleNextReport() {
+  DCHECK(!is_flushing_);
+
   DVLOG(1) << "Scheduling next report in " << report_interval_.InSeconds()
            << "seconds.";
   timer_.Start(FROM_HERE, report_interval_, this,
@@ -91,44 +104,70 @@ void LegacyMetricsClient::Report(
     }
   }
 
-  if (events.empty()) {
-    ScheduleNextReport();
-    return;
-  }
+  std::move(events.begin(), events.end(), std::back_inserter(to_send_));
 
-  DrainBuffer(std::move(events));
+  DrainBuffer();
 }
 
-void LegacyMetricsClient::DrainBuffer(
-    std::vector<fuchsia::legacymetrics::Event> buffer) {
-  if (buffer.empty()) {
+void LegacyMetricsClient::DrainBuffer() {
+  DVLOG(1) << __func__ << " called.";
+
+  if (record_ack_pending_) {
+    // There is a Record() call already inflight. When it is acknowledged,
+    // buffer draining will continue.
+    return;
+  }
+
+  if (to_send_.empty()) {
     DVLOG(1) << "Buffer drained.";
-    ScheduleNextReport();
+
+    if (is_flushing_) {
+      metrics_recorder_.Unbind();
+    } else {
+      ScheduleNextReport();
+    }
+
     return;
   }
 
-  // Since ordering doesn't matter, we can efficiently drain |buffer| by
+  // Since ordering doesn't matter, we can efficiently drain |to_send_| by
   // repeatedly sending and truncating its tail.
-  const size_t batch_size = std::min(buffer.size(), kMaxBatchSize);
-  const size_t batch_start_idx = buffer.size() - batch_size;
+  const size_t batch_size = std::min(to_send_.size(), kMaxBatchSize);
+  const size_t batch_start_idx = to_send_.size() - batch_size;
   std::vector<fuchsia::legacymetrics::Event> batch;
   batch.resize(batch_size);
-  std::move(buffer.begin() + batch_start_idx, buffer.end(), batch.begin());
-  buffer.resize(buffer.size() - batch_size);
-
-  metrics_recorder_->Record(std::move(batch),
-                            [this, buffer = std::move(buffer)]() mutable {
-                              DrainBuffer(std::move(buffer));
-                            });
+  std::move(to_send_.begin() + batch_start_idx, to_send_.end(), batch.begin());
+  to_send_.resize(to_send_.size() - batch_size);
+
+  record_ack_pending_ = true;
+  metrics_recorder_->Record(std::move(batch), [this]() {
+    record_ack_pending_ = false;
+    DrainBuffer();
+  });
 }
 
 void LegacyMetricsClient::OnMetricsRecorderDisconnected(zx_status_t status) {
-  ZX_LOG_IF(ERROR, status != ZX_ERR_PEER_CLOSED, status)
-      << "MetricsRecorder connection lost.";
+  ZX_LOG(ERROR, status) << "MetricsRecorder connection lost.";
 
   // Stop recording & reporting user events.
   user_events_recorder_.reset();
   timer_.AbandonAndStop();
 }
 
+void LegacyMetricsClient::OnCloseSoon() {
+  DVLOG(1) << __func__ << " called.";
+
+  timer_.AbandonAndStop();
+
+  is_flushing_ = true;
+  if (notify_flush_callback_) {
+    // Defer reporting until the flush operation has finished.
+    std::move(notify_flush_callback_)
+        .Run(base::BindOnce(&LegacyMetricsClient::StartReport,
+                            weak_factory_.GetWeakPtr()));
+  } else {
+    StartReport();
+  }
+}
+
 }  // namespace cr_fuchsia
diff --git a/chromium/fuchsia/base/legacymetrics_client.h b/chromium/fuchsia/base/legacymetrics_client.h
index 98576a1f410..b9ec76a2a1f 100644
--- a/chromium/fuchsia/base/legacymetrics_client.h
+++ b/chromium/fuchsia/base/legacymetrics_client.h
@@ -31,6 +31,8 @@ class LegacyMetricsClient {
 
   using ReportAdditionalMetricsCallback = base::RepeatingCallback<void(
       base::OnceCallback<void(std::vector<fuchsia::legacymetrics::Event>)>)>;
+  using NotifyFlushCallback =
+      base::OnceCallback<void(base::OnceClosure completion_cb)>;
 
   LegacyMetricsClient();
   ~LegacyMetricsClient();
@@ -50,18 +52,27 @@ class LegacyMetricsClient {
   void SetReportAdditionalMetricsCallback(
       ReportAdditionalMetricsCallback callback);
 
+  // Sets a |callback| which is invoked to warn that the connection to the
+  // remote MetricsRecorder will be terminated. The completion closure passed to
+  // |callback| should be invoked to signal flush completion.
+  void SetNotifyFlushCallback(NotifyFlushCallback callback);
+
  private:
   void ScheduleNextReport();
   void StartReport();
   void Report(std::vector<fuchsia::legacymetrics::Event> additional_metrics);
   void OnMetricsRecorderDisconnected(zx_status_t status);
+  void OnCloseSoon();
 
-  // Incrementally sends the contents of |buffer| to |metrics_recorder|, and
-  // invokes |done_cb| when finished.
-  void DrainBuffer(std::vector<fuchsia::legacymetrics::Event> buffer);
+  // Incrementally sends the contents of |to_send_| to |metrics_recorder_|.
+  void DrainBuffer();
 
   base::TimeDelta report_interval_;
   ReportAdditionalMetricsCallback report_additional_callback_;
+  NotifyFlushCallback notify_flush_callback_;
+  bool is_flushing_ = false;
+  bool record_ack_pending_ = false;
+  std::vector<fuchsia::legacymetrics::Event> to_send_;
   std::unique_ptr<LegacyMetricsUserActionRecorder> user_events_recorder_;
 
   fuchsia::legacymetrics::MetricsRecorderPtr metrics_recorder_;
diff --git a/chromium/fuchsia/base/legacymetrics_client_unittest.cc b/chromium/fuchsia/base/legacymetrics_client_unittest.cc
index 8c735bbbffe..1b48827418a 100644
--- a/chromium/fuchsia/base/legacymetrics_client_unittest.cc
+++ b/chromium/fuchsia/base/legacymetrics_client_unittest.cc
@@ -14,6 +14,7 @@
 #include "base/threading/thread_task_runner_handle.h"
 #include "fuchsia/base/legacymetrics_client.h"
 #include "fuchsia/base/legacymetrics_histogram_flattener.h"
+#include "fuchsia/base/result_receiver.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace cr_fuchsia {
@@ -45,10 +46,21 @@ class TestMetricsRecorder
     ack_callback_ = base::nullopt;
   }
 
+  void set_expect_ack_dropped(bool expect_dropped) {
+    expect_ack_dropped_ = expect_dropped;
+  }
+
   // fuchsia::legacymetrics::MetricsRecorder implementation.
   void Record(std::vector<fuchsia::legacymetrics::Event> events,
               RecordCallback callback) override {
-    recorded_events_ = std::move(events);
+    std::move(events.begin(), events.end(),
+              std::back_inserter(recorded_events_));
+
+    // Received a call to Record() before the previous one was acknowledged,
+    // which can happen in some cases (e.g. flushing).
+    if (ack_callback_)
+      EXPECT_TRUE(expect_ack_dropped_);
+
     ack_callback_ = std::move(callback);
 
     if (on_record_cb_)
@@ -61,6 +73,7 @@ class TestMetricsRecorder
   std::vector<fuchsia::legacymetrics::Event> recorded_events_;
   base::OnceClosure on_record_cb_;
   base::Optional<RecordCallback> ack_callback_;
+  bool expect_ack_dropped_ = false;
 };
 
 class LegacyMetricsClientTest : public testing::Test {
@@ -71,9 +84,10 @@ class LegacyMetricsClientTest : public testing::Test {
   ~LegacyMetricsClientTest() override = default;
 
   void SetUp() override {
-    service_binding_ = std::make_unique<base::fuchsia::ScopedServiceBinding<
-        fuchsia::legacymetrics::MetricsRecorder>>(
-        test_context_.additional_services(), &test_recorder_);
+    service_binding_ =
+        std::make_unique<base::fuchsia::ScopedSingleClientServiceBinding<
+            fuchsia::legacymetrics::MetricsRecorder>>(
+            test_context_.additional_services(), &test_recorder_);
     base::SetRecordActionTaskRunner(base::ThreadTaskRunnerHandle::Get());
 
     // Flush any dirty histograms from previous test runs in this process.
@@ -84,7 +98,7 @@ class LegacyMetricsClientTest : public testing::Test {
   base::test::TaskEnvironment task_environment_;
   base::TestComponentContextForProcess test_context_;
   TestMetricsRecorder test_recorder_;
-  std::unique_ptr<base::fuchsia::ScopedServiceBinding<
+  std::unique_ptr<base::fuchsia::ScopedSingleClientServiceBinding<
       fuchsia::legacymetrics::MetricsRecorder>>
       service_binding_;
   LegacyMetricsClient client_;
@@ -216,5 +230,92 @@ TEST_F(LegacyMetricsClientTest, Batching) {
   test_recorder_.SendAck();
 }
 
+TEST_F(LegacyMetricsClientTest, FlushWithPending) {
+  client_.Start(kReportInterval);
+  base::RunLoop().RunUntilIdle();
+
+  UMA_HISTOGRAM_COUNTS_1M("foo", 20);
+
+  EXPECT_FALSE(test_recorder_.IsRecordInFlight());
+  service_binding_->events().OnCloseSoon();
+  base::RunLoop().RunUntilIdle();
+  EXPECT_TRUE(test_recorder_.IsRecordInFlight());
+
+  // The service should be unbound once all data is drained.
+  EXPECT_TRUE(service_binding_->has_clients());
+  auto events = test_recorder_.WaitForEvents();
+  test_recorder_.SendAck();
+  base::RunLoop().RunUntilIdle();
+  EXPECT_EQ(1u, events.size());
+  EXPECT_EQ("foo", events[0].histogram().name());
+  EXPECT_FALSE(service_binding_->has_clients());
+}
+
+TEST_F(LegacyMetricsClientTest, FlushNoData) {
+  client_.Start(kReportInterval);
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_TRUE(service_binding_->has_clients());
+  EXPECT_FALSE(test_recorder_.IsRecordInFlight());
+  service_binding_->events().OnCloseSoon();
+  base::RunLoop().RunUntilIdle();
+  EXPECT_FALSE(service_binding_->has_clients());
+}
+
+TEST_F(LegacyMetricsClientTest, FlushWithOutstandingAck) {
+  client_.Start(kReportInterval);
+  base::RunLoop().RunUntilIdle();
+
+  // Send "foo", but don't ack.
+  UMA_HISTOGRAM_COUNTS_1M("foo", 20);
+  task_environment_.FastForwardBy(kReportInterval);
+  EXPECT_TRUE(test_recorder_.IsRecordInFlight());
+
+  // Allow the flush operation to call Record() without waiting for a prior ack.
+  test_recorder_.set_expect_ack_dropped(true);
+
+  // Buffer another event and trigger a flush.
+  UMA_HISTOGRAM_COUNTS_1M("bar", 20);
+  EXPECT_TRUE(service_binding_->has_clients());
+  service_binding_->events().OnCloseSoon();
+
+  // Simulate an asynchronous ack from the recorder, which be delivered around
+  // the same time as the flush's Record() call. The ack should be gracefully
+  // ignored by the client.
+  test_recorder_.SendAck();
+
+  base::RunLoop().RunUntilIdle();
+
+  auto events = test_recorder_.WaitForEvents();
+  test_recorder_.SendAck();
+  base::RunLoop().RunUntilIdle();
+  EXPECT_EQ(2u, events.size());
+  EXPECT_EQ("foo", events[0].histogram().name());
+  EXPECT_EQ("bar", events[1].histogram().name());
+  EXPECT_FALSE(service_binding_->has_clients());
+}
+
+TEST_F(LegacyMetricsClientTest, ExternalFlushSignal) {
+  ResultReceiver<base::OnceClosure> flush_receiver;
+  client_.SetNotifyFlushCallback(flush_receiver.GetReceiveCallback());
+  client_.Start(kReportInterval);
+  base::RunLoop().RunUntilIdle();
+
+  UMA_HISTOGRAM_COUNTS_1M("foo", 20);
+
+  // Verify that reporting does not start until the flush completion callback is
+  // run.
+  EXPECT_FALSE(test_recorder_.IsRecordInFlight());
+  service_binding_->events().OnCloseSoon();
+  base::RunLoop().RunUntilIdle();
+  EXPECT_FALSE(test_recorder_.IsRecordInFlight());
+
+  // Verify that invoking the completion callback unblocks reporting.
+  EXPECT_TRUE(flush_receiver.has_value());
+  std::move(*flush_receiver).Run();
+  base::RunLoop().RunUntilIdle();
+  EXPECT_TRUE(test_recorder_.IsRecordInFlight());
+}
+
 }  // namespace
 }  // namespace cr_fuchsia
diff --git a/chromium/fuchsia/base/legacymetrics_histogram_flattener.cc b/chromium/fuchsia/base/legacymetrics_histogram_flattener.cc
index e05d87ced9a..b6d728143c1 100644
--- a/chromium/fuchsia/base/legacymetrics_histogram_flattener.cc
+++ b/chromium/fuchsia/base/legacymetrics_histogram_flattener.cc
@@ -8,6 +8,7 @@
 #include <utility>
 #include <vector>
 
+#include "base/logging.h"
 #include "base/metrics/statistics_recorder.h"
 
 namespace cr_fuchsia {