Add tooltip for comment toggle in diff. Add changelog item and fix tests

CHANGELOG

@@ -6,6 +6,7 @@ v 7.10.0 (unreleased)
   - Add a service to support external wikis (Hannes Rosenögger)
   - List new commits for newly pushed branch in activity view.
   - Add changelog, license and contribution guide links to project sidebar.
+  - Improve diff UI
 
 v 7.9.0 (unreleased)
   - Add HipChat integration documentation (Stan Hu)

app/views/projects/diffs/_file.html.haml

@@ -22,7 +22,7 @@
 
       .diff-btn-group
         - if blob.text?
-          = link_to '#', class: 'js-toggle-diff-comments btn btn-sm active' do
+          = link_to '#', class: 'js-toggle-diff-comments btn btn-sm active has_tooltip', title: "Toggle comments for this file" do
             %i.fa.fa-comments
            
 

features/steps/project/merge_requests.rb

@@ -209,13 +209,13 @@ class Spinach::Features::ProjectMergeRequests < Spinach::FeatureSteps
 
   step 'I click link "Hide inline discussion" of the second file' do
     within '.files [id^=diff]:nth-child(2)' do
-      click_link 'Show/Hide comments'
+      find('.js-toggle-diff-comments').click
     end
   end
 
   step 'I click link "Show inline discussion" of the second file' do
     within '.files [id^=diff]:nth-child(2)' do
-      click_link 'Show/Hide comments'
+      find('.js-toggle-diff-comments').click
     end
   end