Delete ash-based code for Windows drag-and-drop graphics.

ui/base/dragdrop/os_exchange_data_provider_mac.mm

 // 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.
 
 #include "ui/base/dragdrop/os_exchange_data_provider_mac.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
@@ skipping 163 matching lines @@
   return [[pasteboard_->get() types] containsObject:format.ToNSString()];
 }
 
 void OSExchangeDataProviderMac::SetDragImage(
     const gfx::ImageSkia& image,
     const gfx::Vector2d& cursor_offset) {
   drag_image_ = image;
   cursor_offset_ = cursor_offset;
 }
 
-const gfx::ImageSkia& OSExchangeDataProviderMac::GetDragImage() const {
+gfx::ImageSkia OSExchangeDataProviderMac::GetDragImage() const {
   return drag_image_;
 }
 
-const gfx::Vector2d& OSExchangeDataProviderMac::GetDragImageOffset() const {
+gfx::Vector2d OSExchangeDataProviderMac::GetDragImageOffset() const {
   return cursor_offset_;
 }
 
 NSData* OSExchangeDataProviderMac::GetNSDataForType(NSString* type) const {
   return [pasteboard_->get() dataForType:type];
 }
 
 // static
 std::unique_ptr<OSExchangeData>
 OSExchangeDataProviderMac::CreateDataFromPasteboard(NSPasteboard* pasteboard) {
@@ skipping 10 matching lines @@
 NSArray* OSExchangeDataProviderMac::SupportedPasteboardTypes() {
   return @[
     kWebCustomDataPboardType, ui::ClipboardUtil::UTIForWebURLsAndTitles(),
     NSURLPboardType, NSFilenamesPboardType, ui::kChromeDragDummyPboardType,
     NSStringPboardType, NSHTMLPboardType, NSRTFPboardType,
     NSFilenamesPboardType, ui::kWebCustomDataPboardType, NSPasteboardTypeString
   ];
 }
 
 }  // namespace ui