Support dragging a virtual file out of the browser.

base/base_drag_source.h

 // Copyright (c) 2006-2008 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.
 
 #ifndef BASE_BASE_DRAG_SOURCE_H_
 #define BASE_BASE_DRAG_SOURCE_H_
 
 #include <objidl.h>
 
 #include "base/basictypes.h"
+#include "base/ref_counted.h"
 
 ///////////////////////////////////////////////////////////////////////////////
 //
 // BaseDragSource
 //
 //  A base IDropSource implementation. Handles notifications sent by an active
 //  drag-drop operation as the user mouses over other drop targets on their
 //  system. This object tells Windows whether or not the drag should continue,
 //  and supplies the appropriate cursors.
 //
-class BaseDragSource : public IDropSource {
+class BaseDragSource : public IDropSource,
+                       public base::RefCountedThreadSafe<BaseDragSource> {
  public:
   BaseDragSource();
   virtual ~BaseDragSource() { }
 
   // Stop the drag operation at the next chance we get.  This doesn't
   // synchronously stop the drag (since Windows is controlling that),
   // but lets us tell Windows to cancel the drag the next chance we get.
   void CancelDrag() {
     cancel_drag_ = true;
   }
 
   // IDropSource implementation:
   HRESULT __stdcall QueryContinueDrag(BOOL escape_pressed, DWORD key_state);
   HRESULT __stdcall GiveFeedback(DWORD effect);
 
   // IUnknown implementation:
   HRESULT __stdcall QueryInterface(const IID& iid, void** object);
   ULONG __stdcall AddRef();
   ULONG __stdcall Release();
 
  protected:
   virtual void OnDragSourceCancel() { }
   virtual void OnDragSourceDrop() { }
   virtual void OnDragSourceMove() { }
 
  private:
-  LONG ref_count_;
-
   // Set to true if we want to cancel the drag operation.
   bool cancel_drag_;
 
   DISALLOW_EVIL_CONSTRUCTORS(BaseDragSource);
 };
 
 #endif  // BASE_BASE_DRAG_SOURCE_H_