Remove findDOMNode in DraftEditorDragHandler

Summary:
As in my previous change, editor.editorContainer is always an element and doesn't need findDOMNode.

https://github.com/facebook/draft-js/blob/822d2fbd3597c3fe20cc2508d6a12d9a6f856999/src/component/base/DraftEditor.react.js#L370

This isn't exactly the same because the previous code got the parent node:

https://github.com/facebook/draft-js/blob/822d2fbd3597c3fe20cc2508d6a12d9a6f856999/src/component/base/DraftEditor.react.js#L366

However for this purpose they're the same. There are no listeners on the inner one and the event bubbles. We already have a ref to the inner one so might as well use it.

Now I think that this has since been fixed in React so we might  not need this workaround at all anymore.

Reviewed By: gaearon

Differential Revision: D19540873

fbshipit-source-id: 89f91105b97ae6b0eeb5b4d615642a79eef6ab92

Author: sebmarkbage

src/component/handlers/drag/DraftEditorDragHandler.js

@@ -17,7 +17,6 @@ import type SelectionState from 'SelectionState';
 const DataTransfer = require('DataTransfer');
 const DraftModifier = require('DraftModifier');
 const EditorState = require('EditorState');
-const ReactDOM = require('ReactDOM');
 
 const findAncestorOffsetKey = require('findAncestorOffsetKey');
 const getCorrectDocumentFromNode = require('getCorrectDocumentFromNode');
@@ -142,7 +141,7 @@ function endDrag(editor) {
   // Prior to React v16.5.0 onDrop breaks onSelect event:
   // https://github.com/facebook/react/issues/11379.
   // Dispatching a mouseup event on DOM node will make it go back to normal.
-  const editorNode = ReactDOM.findDOMNode(editor);
+  const editorNode = editor.editorContainer;
   if (editorNode) {
     const mouseUpEvent = new MouseEvent('mouseup', {
       view: getWindowForNode(editorNode),