Fix dom shims to support rich_content_editor

- Remove mutation observer shim since
  this is an incomplete API
- Remove our custom Range support since
  this was already added by jsdom
- Extend the Range.prototype with missing
  methods

spec/frontend/environment.js

@@ -50,16 +50,6 @@ class CustomEnvironment extends JSDOMEnvironment {
      */
     this.global.fetch = () => {};
 
-    // Not yet supported by JSDOM: https://github.com/jsdom/jsdom/issues/317
-    this.global.document.createRange = () => ({
-      setStart: () => {},
-      setEnd: () => {},
-      commonAncestorContainer: {
-        nodeName: 'BODY',
-        ownerDocument: this.global.document,
-      },
-    });
-
     // Expose the jsdom (created in super class) to the global so that we can call reconfigure({ url: '' }) to properly set `window.location`
     this.global.dom = this.dom;
   }

spec/frontend/helpers/dom_shims/index.js

@@ -4,7 +4,7 @@ import './element_scroll_to';
 import './form_element';
 import './get_client_rects';
 import './inner_text';
-import './mutation_observer';
+import './range';
 import './window_scroll_to';
 import './scroll_by';
 import './size_properties';

spec/frontend/helpers/dom_shims/mutation_observer.js

-/* eslint-disable class-methods-use-this */
-class MutationObserverStub {
-  disconnect() {}
-  observe() {}
-}
-
-global.MutationObserver = MutationObserverStub;

spec/frontend/helpers/dom_shims/range.js

+if (window.Range.prototype.getBoundingClientRect) {
+  throw new Error('window.Range.prototype.getBoundingClientRect already exists. Remove this stub!');
+}
+window.Range.prototype.getBoundingClientRect = function getBoundingClientRect() {
+  return { x: 0, y: 0, width: 0, height: 0, top: 0, right: 0, bottom: 0, left: 0 };
+};
+
+if (window.Range.prototype.getClientRects) {
+  throw new Error('window.Range.prototype.getClientRects already exists. Remove this stub!');
+}
+window.Range.prototype.getClientRects = function getClientRects() {
+  return [this.getBoundingClientRect()];
+};

spec/frontend/vue_shared/components/rich_content_editor/rich_content_editor_integration_spec.js

 import Editor from '@toast-ui/editor';
 import { registerHTMLToMarkdownRenderer } from '~/vue_shared/components/rich_content_editor/services/editor_service';
-import '@toast-ui/editor/dist/toastui-editor.css';
 
 describe('vue_shared/components/rich_content_editor', () => {
   let editor;
@@ -18,7 +17,6 @@ describe('vue_shared/components/rich_content_editor', () => {
   });
 
   describe('HTML to Markdown', () => {
-
     it('uses "-" character list marker in unordered lists', () => {
       editor.setHtml('<ul><li>List item 1</li><li>List item 2</li></ul>');