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

ui/views/cocoa/drag_drop_client_mac.mm

 // Copyright 2016 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.
 
 #import "ui/views/cocoa/drag_drop_client_mac.h"
 
 #include "base/mac/mac_util.h"
 #include "base/run_loop.h"
 #include "base/strings/sys_string_conversions.h"
 #import "ui/base/dragdrop/os_exchange_data_provider_mac.h"
 #include "ui/gfx/image/image_skia_util_mac.h"
 #include "ui/views/drag_utils.h"
 #import "ui/views/cocoa/bridged_content_view.h"
 #import "ui/views/cocoa/bridged_native_widget.h"
 #include "ui/views/widget/native_widget_mac.h"
 
 @interface CocoaDragDropDataProvider ()
 - (id)initWithData:(const ui::OSExchangeData&)data;
 - (id)initWithPasteboard:(NSPasteboard*)pasteboard;
 @end
 
 @implementation CocoaDragDropDataProvider {
   std::unique_ptr<ui::OSExchangeData> data_;
 }
 
 - (id)initWithData:(const ui::OSExchangeData&)data {
   if ((self = [super init])) {
-    data_.reset(new OSExchangeData(data.provider().Clone()));
+    data_.reset(new OSExchangeData(
+        std::unique_ptr<OSExchangeData::Provider>(data.provider().Clone())));
   }
   return self;
 }
 
 - (id)initWithPasteboard:(NSPasteboard*)pasteboard {
   if ((self = [super init])) {
     data_ = ui::OSExchangeDataProviderMac::CreateDataFromPasteboard(pasteboard);
   }
   return self;
 }
@@ skipping 115 matching lines @@
     quit_closure_.Run();
     quit_closure_.Reset();
   }
 }
 
 gfx::Point DragDropClientMac::LocationInView(NSPoint point) const {
   return gfx::Point(point.x, NSHeight([bridge_->ns_window() frame]) - point.y);
 }
 
 }  // namespace views