Improve drag-and-drop comment in MouseEventManager.

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 883 matching lines @@
   if (dragState().m_dragDataTransfer) {
     dragState().m_dragDataTransfer->clearDragImage();
     dragState().m_dragDataTransfer->setAccessPolicy(DataTransferNumb);
   }
 }
 
 void MouseEventManager::dragSourceEndedAt(const PlatformMouseEvent& event,
                                           DragOperation operation) {
   if (dragState().m_dragSrc) {
     dragState().m_dragDataTransfer->setDestinationOperation(operation);
-    // For now we don't care if event handler cancels default behavior, since
-    // there is none.
+    // The return value is ignored because dragend is not cancelable.
     dispatchDragSrcEvent(EventTypeNames::dragend, event);
   }
   clearDragDataTransfer();
   dragState().m_dragSrc = nullptr;
   // In case the drag was ended due to an escape key press we need to ensure
   // that consecutive mousemove events don't reinitiate the drag and drop.
   m_mouseDownMayStartDrag = false;
 }
 
 DragState& MouseEventManager::dragState() {
@@ skipping 71 matching lines @@
 
 void MouseEventManager::setClickCount(int clickCount) {
   m_clickCount = clickCount;
 }
 
 bool MouseEventManager::mouseDownMayStartDrag() {
   return m_mouseDownMayStartDrag;
 }
 
 }  // namespace blink