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

ui/base/dragdrop/os_exchange_data_provider_mac.h

 // Copyright 2014 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_MAC_H_
 #define UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_MAC_H_
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #import "ui/base/clipboard/clipboard_util_mac.h"
@@ skipping 10 matching lines @@
 class UniquePasteboard;
 
 // OSExchangeData::Provider implementation for Mac.
 class UI_BASE_EXPORT OSExchangeDataProviderMac
     : public OSExchangeData::Provider {
  public:
   OSExchangeDataProviderMac();
   ~OSExchangeDataProviderMac() override;
 
   // 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& data) override;
   bool GetString(base::string16* data) const override;
   bool GetURLAndTitle(OSExchangeData::FilenameToURLPolicy policy,
@@ skipping 30 matching lines @@
   // Drag image and offset data.
   gfx::ImageSkia drag_image_;
   gfx::Vector2d cursor_offset_;
 
   DISALLOW_COPY_AND_ASSIGN(OSExchangeDataProviderMac);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_DRAGDROP_OS_EXCHANGE_DATA_PROVIDER_MAC_H_