Check detached status before attempting to clear drag transfer state (reland.)

third_party/WebKit/Source/core/input/MouseEventManager.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/input/MouseEventManager.h"
 
 #include "core/clipboard/DataObject.h"
 #include "core/clipboard/DataTransfer.h"
 #include "core/dom/Element.h"
 #include "core/dom/ElementTraversal.h"
@@ skipping 927 matching lines @@
       MouseEvent::webInputEventModifiersToButtons(event.modifiers()), nullptr,
       TimeTicks::FromSeconds(event.timeStampSeconds()), dataTransfer,
       event.fromTouch() ? MouseEvent::FromTouch
                         : MouseEvent::RealOrIndistinguishable);
 
   return EventHandlingUtil::toWebInputEventResult(
       dragTarget->dispatchEvent(me));
 }
 
 void MouseEventManager::clearDragDataTransfer() {
+  if (!m_frame->page())
+    return;
   if (dragState().m_dragDataTransfer) {
     dragState().m_dragDataTransfer->clearDragImage();
     dragState().m_dragDataTransfer->setAccessPolicy(DataTransferNumb);
   }
 }
 
 void MouseEventManager::dragSourceEndedAt(const WebMouseEvent& event,
                                           DragOperation operation) {
   if (dragState().m_dragSrc) {
     dragState().m_dragDataTransfer->setDestinationOperation(operation);
@@ skipping 88 matching lines @@
 
 void MouseEventManager::setClickCount(int clickCount) {
   m_clickCount = clickCount;
 }
 
 bool MouseEventManager::mouseDownMayStartDrag() {
   return m_mouseDownMayStartDrag;
 }
 
 }  // namespace blink