[MD Bookmarks] Fix Drag and drop timer.

This CL fixes a misnamed member in the drag and drop manager.

BUG=716257
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2853973002
Cr-Commit-Position: refs/heads/master@{#468578}

chrome/browser/resources/md_bookmarks/dnd_manager.js

@@ -287,7 +287,7 @@ cr.define('bookmarks', function() {
      * Used to instantly clearDragData in tests.
      * @private {function((Function|null|string), number)}
      */
-    this.setTimeout = window.setTimeout.bind(window);
+    this.setTimeout_ = window.setTimeout.bind(window);
   }
 
   DNDManager.prototype = {