Allow OSExchangeData::Provider to be overridden at run time.

ui/base/dragdrop/os_exchange_data_provider_aurax11.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_PROVIDER_AURAX11_H_
 #define UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_AURAX11_H_
 
 #include <stdint.h>
 #include <X11/Xlib.h>
 
@@ skipping 45 matching lines @@
   void RetrieveTargets(std::vector<Atom>* targets) const;
 
   // Makes a copy of the format map currently being offered.
   SelectionFormatMap GetFormatMap() const;
 
   const base::FilePath& file_contents_name() const {
     return file_contents_name_;
   }
 
   // Overridden from OSExchangeData::Provider:
-  Provider* Clone() const override;
+  std::unique_ptr<Provider> Clone() const override;
   void MarkOriginatedFromRenderer() override;
   bool DidOriginateFromRenderer() const override;
   void SetString(const base::string16& data) override;
   void SetURL(const GURL& url, const base::string16& title) override;
   void SetFilename(const base::FilePath& path) override;
   void SetFilenames(const std::vector<FileInfo>& filenames) override;
   void SetPickledData(const Clipboard::FormatType& format,
                       const base::Pickle& pickle) override;
   bool GetString(base::string16* data) const override;
   bool GetURLAndTitle(OSExchangeData::FilenameToURLPolicy policy,
@@ skipping 64 matching lines @@
 
   // Takes a snapshot of |format_map_| and offers it to other windows.
   mutable SelectionOwner selection_owner_;
 
   DISALLOW_COPY_AND_ASSIGN(OSExchangeDataProviderAuraX11);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_AURAX11_H_