Don't pick a drop operation that the source doesn't support.

third_party/WebKit/Source/core/page/DragController.cpp

 /*
  * Copyright (C) 2007, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 562 matching lines @@
 }
 
 static DragOperation defaultOperationForDrag(DragOperation srcOpMask)
 {
     // This is designed to match IE's operation fallback for the case where
     // the page calls preventDefault() in a drag event but doesn't set dropEffect.
     if (srcOpMask == DragOperationEvery)
         return DragOperationCopy;
     if (srcOpMask == DragOperationNone)
         return DragOperationNone;
-    if (srcOpMask & DragOperationMove || srcOpMask & DragOperationGeneric)
+    if (srcOpMask & DragOperationMove)
         return DragOperationMove;
     if (srcOpMask & DragOperationCopy)
         return DragOperationCopy;
     if (srcOpMask & DragOperationLink)
         return DragOperationLink;
 
     // FIXME: Does IE really return "generic" even if no operations were allowed by the source?
     return DragOperationGeneric;
 }
 
@@ skipping 398 matching lines @@
 
 DEFINE_TRACE(DragController)
 {
     visitor->trace(m_page);
     visitor->trace(m_documentUnderMouse);
     visitor->trace(m_dragInitiator);
     visitor->trace(m_fileInputElementUnderMouse);
 }
 
 } // namespace blink