Fix deadlock between UI thread and drag and drop thread on Windows.

ui/base/dragdrop/os_exchange_data.h

 // Copyright (c) 2012 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 UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_H_
 #define UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_H_
 
 #include "build/build_config.h"
 
 #include <set>
@@ skipping 117 matching lines @@
     virtual bool HasCustomFormat(
         OSExchangeData::CustomFormat format) const = 0;
 
 #if defined(OS_WIN)
     virtual void SetFileContents(const base::FilePath& filename,
                                  const std::string& file_contents) = 0;
     virtual bool GetFileContents(base::FilePath* filename,
                                  std::string* file_contents) const = 0;
     virtual bool HasFileContents() const = 0;
     virtual void SetDownloadFileInfo(const DownloadFileInfo& download) = 0;
+    virtual void SetInDragLoop(bool in_drag_loop) = 0;
 #endif
 
 #if defined(OS_WIN) || defined(USE_AURA)
     virtual void SetHtml(const string16& html, const GURL& base_url) = 0;
     virtual bool GetHtml(string16* html, GURL* base_url) const = 0;
     virtual bool HasHtml() const = 0;
 #endif
 
 #if defined(USE_AURA)
     virtual void SetDragImage(const gfx::ImageSkia& image,
@@ skipping 72 matching lines @@
 
 #if defined(OS_WIN)
   // Adds the bytes of a file (CFSTR_FILECONTENTS and CFSTR_FILEDESCRIPTOR).
   void SetFileContents(const base::FilePath& filename,
                        const std::string& file_contents);
   bool GetFileContents(base::FilePath* filename,
                        std::string* file_contents) const;
 
   // Adds a download file with full path (CF_HDROP).
   void SetDownloadFileInfo(const DownloadFileInfo& download);
+
+  void SetInDragLoop(bool in_drag_loop);
 #endif
 
 #if defined(OS_WIN) || defined(USE_AURA)
   // Adds a snippet of HTML.  |html| is just raw html but this sets both
   // text/html and CF_HTML.
   void SetHtml(const string16& html, const GURL& base_url);
   bool GetHtml(string16* html, GURL* base_url) const;
 #endif
 
  private:
   // Provides the actual data.
   scoped_ptr<Provider> provider_;
 
   DISALLOW_COPY_AND_ASSIGN(OSExchangeData);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_H_