[MD Bookmarks] Clear internal drag when native drag starts.

Bug: 748445
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I5d10fdd84b302a3064056f73544d8c214aace2bd
Reviewed-on: https://chromium-review.googlesource.com/584558Reviewed-by: Tim Sergeant <tsergeant@chromium.org>
Commit-Queue: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#491167}

chrome/browser/resources/md_bookmarks/dnd_manager.js

@@ -635,7 +635,6 @@ cr.define('bookmarks', function() {
      */
     startNativeDrag_: function() {
       var state = bookmarks.Store.getInstance().data;
-      this.dndChip.hide();
 
       if (!this.dragInfo_.isDragValid())
         return false;
@@ -643,6 +642,10 @@ cr.define('bookmarks', function() {
       var draggedNodes =
           this.dragInfo_.dragData.elements.map((item) => item.id);
 
+      // Clear the drag data here so that the chip is hidden. The native drag
+      // will return after the clearing and set up its data.
+      this.clearDragData_();
+
       // TODO(calamity): account for touch.
       chrome.bookmarkManagerPrivate.startDrag(draggedNodes, false);
 

chrome/test/data/webui/md_bookmarks/dnd_manager_test.js

@@ -383,6 +383,7 @@ suite('drag and drop', function() {
     assertDeepEquals(['13'], getDragIds());
 
     dispatchDragEvent('dragstart', dragElement);
+    assertEquals(null, dndManager.internalDragElement_);
     assertDeepEquals(['13'], draggedIds);
     dndManager.handleChromeDragEnter_(createDragData(draggedIds));