Merge branch '23520-mr-sticky-tabs-overlap-discussion-from-anchor' into 'master'

Account for fixed position MR when scrolling to elements

## What does this MR do?

This MR accounts for the new merge request fixed affix bar when scrolling to an element on the MR page.

## Are there points in the code the reviewer needs to double check?

## Why was this MR needed?

The fixed MR tabs bar was not being taken into account when shifting permalink scroll targets so that they are unobscured by navigation elements.

## Screenshots (if relevant)

Issues discussion permalink:
![Screen_Shot_2016-10-26_at_12.29.26_AM](/uploads/e278f784252f2b79c466f56b4f36d198/Screen_Shot_2016-10-26_at_12.29.26_AM.png)

Merge request discussion permalink:
![Screen_Shot_2016-10-26_at_12.28.26_AM](/uploads/1e57357fffb815b217484f09377f3c23/Screen_Shot_2016-10-26_at_12.28.26_AM.png)

Merge request diff permalink:
![Screen_Shot_2016-10-26_at_12.29.02_AM](/uploads/269f3a4a4075932355f665322387db86/Screen_Shot_2016-10-26_at_12.29.02_AM.png)

Commit diff page permalinks work as well, but aren't highlighted currently (see: #23696)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #23520

See merge request !7051

app/assets/javascripts/application.js

@@ -58,11 +58,28 @@
   document.addEventListener('page:fetch', gl.utils.cleanupBeforeFetch);
   window.addEventListener('hashchange', gl.utils.shiftWindow);
 
+  // automatically adjust scroll position for hash urls taking the height of the navbar into account
+  // https://github.com/twitter/bootstrap/issues/1768
+  window.adjustScroll = function() {
+    var navbar = document.querySelector('.navbar-gitlab');
+    var subnav = document.querySelector('.layout-nav');
+    var fixedTabs = document.querySelector('.js-tabs-affix');
+
+    adjustment = 0;
+    if (navbar) adjustment -= navbar.offsetHeight;
+    if (subnav) adjustment -= subnav.offsetHeight;
+    if (fixedTabs) adjustment -= fixedTabs.offsetHeight;
+
+    return scrollBy(0, adjustment);
+  };
+
+  window.addEventListener("hashchange", adjustScroll);
+
   window.onload = function () {
     // Scroll the window to avoid the topnav bar
     // https://github.com/twitter/bootstrap/issues/1768
     if (location.hash) {
-      return setTimeout(gl.utils.shiftWindow, 100);
+      return setTimeout(adjustScroll, 100);
     }
   };
 

app/assets/javascripts/merge_request_tabs.js

@@ -130,7 +130,7 @@
     MergeRequestTabs.prototype.scrollToElement = function(container) {
       var $el, navBarHeight;
       if (window.location.hash) {
-        navBarHeight = $('.navbar-gitlab').outerHeight() + $('.layout-nav').outerHeight();
+        navBarHeight = $('.navbar-gitlab').outerHeight() + $('.layout-nav').outerHeight() + document.querySelector('.js-tabs-affix').offsetHeight;
         $el = $(container + " " + window.location.hash + ":not(.match)");
         if ($el.length) {
           return $.scrollTo(container + " " + window.location.hash + ":not(.match)", {