Support dragging a virtual file out of the browser.

base/base_drag_source.cc

 // 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.
 
 #include "base/base_drag_source.h"
 
 ///////////////////////////////////////////////////////////////////////////////
 // BaseDragSource, public:
 
-BaseDragSource::BaseDragSource() : ref_count_(0), cancel_drag_(false) {
+BaseDragSource::BaseDragSource() : cancel_drag_(false) {
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 // BaseDragSource, IDropSource implementation:
 
 HRESULT BaseDragSource::QueryContinueDrag(BOOL escape_pressed,
                                           DWORD key_state) {
   if (cancel_drag_)
     return DRAGDROP_S_CANCEL;
 
@@ skipping 23 matching lines @@
   if (IsEqualIID(iid, IID_IUnknown) || IsEqualIID(iid, IID_IDropSource)) {
     *object = this;
   } else {
     return E_NOINTERFACE;
   }
   AddRef();
   return S_OK;
 }
 
 ULONG BaseDragSource::AddRef() {
-  return ++ref_count_;
+  base::RefCountedThreadSafe<BaseDragSource>::AddRef();
+  return 0;
 }
 
 ULONG BaseDragSource::Release() {
-  if (--ref_count_ == 0) {
-    delete this;
-    return 0U;
-  }
-  return ref_count_;
+  base::RefCountedThreadSafe<BaseDragSource>::Release();
+  return 0;
 }