Fix isHTMLBRElement check

Summary: When rendering in an `iframe`/other document, I was getting an error when trying to add a newline. Turns out there was an issue with the `isHTMLBRElement` check, so fix that and change the code in `DraftEditorLeaf.react.js` to use `isHTMLBRElement`

Reviewed By: claudiopro

Differential Revision: D18815600

fbshipit-source-id: 6297e29efa987e1e6937b5093d565355c5839b2e

src/component/contents/DraftEditorLeaf.react.js

@@ -19,6 +19,7 @@ const DraftEditorTextNode = require('DraftEditorTextNode.react');
 const React = require('React');
 
 const invariant = require('invariant');
+const isHTMLBRElement = require('isHTMLBRElement');
 const setDraftEditorSelection = require('setDraftEditorSelection');
 
 type Props = {
@@ -101,7 +102,7 @@ class DraftEditorLeaf extends React.Component<Props> {
 
     if (child.nodeType === Node.TEXT_NODE) {
       targetNode = child;
-    } else if (child instanceof Element && child.tagName === 'BR') {
+    } else if (isHTMLBRElement(child)) {
       targetNode = node;
     } else {
       targetNode = child.firstChild;

src/component/utils/isElement.js

@@ -5,7 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  * @emails oncall+draft_js
  */
 

src/component/utils/isHTMLBRElement.js

@@ -5,21 +5,17 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @flow strict-local
+ * @flow strict
  * @emails oncall+draft_js
  */
 
+const isElement = require('isElement');
+
 function isHTMLBRElement(node: ?Node): boolean {
   if (!node || !node.ownerDocument) {
     return false;
   }
-  if (!node.ownerDocument.defaultView) {
-    return node instanceof HTMLBRElement;
-  }
-  if (node instanceof node.ownerDocument.defaultView.HTMLElement) {
-    return true;
-  }
-  return false;
+  return isElement(node) && node.nodeName === 'BR';
 }
 
 module.exports = isHTMLBRElement;