Use `Gitlab::Access` to protected branch access levels.

1. It makes sense to reuse these constants since we had them duplicated
   in the previous enum implementation. This also simplifies our
   `check_access` implementation, because we can use
   `project.team.max_member_access` directly.

2. Use `accepts_nested_attributes_for` to create push/merge access
   levels. This was a bit fiddly to set up, but this simplifies our code
   by quite a large amount. We can even get rid of
   `ProtectedBranches::BaseService`.

3. Move API handling back into the API (previously in
   `ProtectedBranches::BaseService#translate_api_params`.

4. The protected branch services now return a `ProtectedBranch` rather
   than `true/false`.

5. Run `load_protected_branches` on-demand in the `create` action, to
   prevent it being called unneccessarily.

6. "Masters" is pre-selected as the default option for "Allowed to Push"
   and "Allowed to Merge".

7. These changes were based on a review from @rymai in !5081.

1 files changed, 14 insertions, 4 deletions

diff --git a/app/assets/javascripts/protected_branches_access_select.js.es6 b/app/assets/javascripts/protected_branches_access_select.js.es6
index 93b7d7755a7..e98312bbf37 100644
--- a/app/assets/javascripts/protected_branches_access_select.js.es6
+++ b/app/assets/javascripts/protected_branches_access_select.js.es6
@@ -1,27 +1,35 @@
 class ProtectedBranchesAccessSelect {
-  constructor(container, saveOnSelect) {
+  constructor(container, saveOnSelect, selectDefault) {
     this.container = container;
     this.saveOnSelect = saveOnSelect;
 
     this.container.find(".allowed-to-merge").each((i, element) => {
       var fieldName = $(element).data('field-name');
-      return $(element).glDropdown({
+      var dropdown = $(element).glDropdown({
         data: gon.merge_access_levels,
         selectable: true,
         fieldName: fieldName,
         clicked: _.chain(this.onSelect).partial(element).bind(this).value()
       });
+
+      if (selectDefault) {
+        dropdown.data('glDropdown').selectRowAtIndex(document.createEvent("Event"), 0);
+      }
     });
 
 
     this.container.find(".allowed-to-push").each((i, element) => {
       var fieldName = $(element).data('field-name');
-      return $(element).glDropdown({
+      var dropdown = $(element).glDropdown({
         data: gon.push_access_levels,
         selectable: true,
         fieldName: fieldName,
         clicked: _.chain(this.onSelect).partial(element).bind(this).value()
       });
+
+      if (selectDefault) {
+        dropdown.data('glDropdown').selectRowAtIndex(document.createEvent("Event"), 0);
+      }
     });
   }
 
@@ -36,7 +44,9 @@ class ProtectedBranchesAccessSelect {
           _method: 'PATCH',
           id: $(dropdown).data('id'),
           protected_branch: {
-            ["" + ($(dropdown).data('type'))]: selected.id
+            ["" + ($(dropdown).data('type')) + "_attributes"]: {
+              "access_level": selected.id
+            }
           }
         },
         success: function() {