Added Sherlock, a custom profiling tool for GitLab

Sherlock will be a new GitLab specific tool for measuring the
performance of Rails requests (and SideKiq jobs at some point). Some of
the things that are currently tracked:

* SQL queries along with their timings, backtraces and query plans
  (using "EXPLAIN ANALYZE" for PostgreSQL and regular "EXPLAIN" for
  MySQL)
* Timings of application files (including views) on a per line basis
* Some meta data such as the request method, path, total duration, etc

More tracking (e.g. Rugged or gitlab-shell timings) might be added in
the future.

Sherlock will replace any existing tools we have used so far (e.g.
active_record_query_trace and rack-mini-profiler), hence the
corresponding Gems have been removed from the Gemfile.

Sherlock can be enabled by starting Rails as following:

    ENABLE_SHERLOCK=1 bundle exec rails s

Recorded transactions can be found at `/sherlock/transactions`.

1 files changed, 27 insertions, 0 deletions

diff --git a/app/views/sherlock/queries/_backtrace.html.haml b/app/views/sherlock/queries/_backtrace.html.haml
new file mode 100644
index 00000000000..5c9294c0ab5
--- /dev/null
+++ b/app/views/sherlock/queries/_backtrace.html.haml
@@ -0,0 +1,27 @@
+.prepend-top-default
+  .panel.panel-default
+    .panel-heading
+      %strong
+        = t('sherlock.application_backtrace')
+    %ul.well-list
+      - @query.application_backtrace.each do |location|
+        %li
+          = location.path
+          %small.light
+            = t('sherlock.line')
+            = location.line
+
+  .panel.panel-default
+    .panel-heading
+      %strong
+        = t('sherlock.full_backtrace')
+    %ul.well-list
+      - @query.backtrace.each do |location|
+        %li
+          - if location.application?
+            %strong= location.path
+          - else
+            = location.path
+          %small.light
+            = t('sherlock.line')
+            = location.line