Fixes blob view not updating highlighted line after hash change

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/213212

app/assets/javascripts/line_highlighter.js

@@ -54,6 +54,7 @@ LineHighlighter.prototype.bindEvents = function() {
 
   $fileHolder.on('click', 'a[data-line-number]', this.clickHandler);
   $fileHolder.on('highlight:line', this.highlightHash);
+  window.addEventListener('hashchange', e => this.highlightHash(e.target.location.hash));
 };
 
 LineHighlighter.prototype.highlightHash = function(newHash) {

spec/javascripts/line_highlighter_spec.js

@@ -67,6 +67,16 @@ describe('LineHighlighter', function() {
 
       expect(func).not.toThrow();
     });
+
+    it('handles hashchange event', () => {
+      const highlighter = new LineHighlighter();
+
+      spyOn(highlighter, 'highlightHash');
+
+      window.dispatchEvent(new Event('hashchange'), 'L15');
+
+      expect(highlighter.highlightHash).toHaveBeenCalled();
+    });
   });
 
   describe('clickHandler', function() {