Moves DragDropClient to aura/client

ui/wm/public/scoped_drag_drop_disabler.cc

 // Copyright 2015 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/wm/public/scoped_drag_drop_disabler.h"
 
+#include "ui/aura/client/drag_drop_client.h"
 #include "ui/aura/window.h"
-#include "ui/wm/public/drag_drop_client.h"
 
 namespace aura {
 namespace client {
 
 class NopDragDropClient : public DragDropClient {
  public:
   ~NopDragDropClient() override {}
   int StartDragAndDrop(const ui::OSExchangeData& data,
                        aura::Window* root_window,
                        aura::Window* source_window,
@@ skipping 27 matching lines @@
 }
 
 void ScopedDragDropDisabler::OnWindowDestroyed(Window* window) {
   CHECK_EQ(window_, window);
   window_ = NULL;
   new_client_.reset();
 }
 
 }  // namespace client
 }  // namespace aura