mash: Use the new mus drag and drop API to get drag working in mash.

ui/views/mus/drag_drop_client_mus.h

+// 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.
+
+#ifndef UI_VIEWS_MUS_DRAG_DROP_CLIENT_MUS_H_
+#define UI_VIEWS_MUS_DRAG_DROP_CLIENT_MUS_H_
+
+#include "ui/base/dragdrop/drag_drop_types.h"
+#include "ui/wm/public/drag_drop_client.h"
+
+namespace aura {
+class Window;
+}
+
+namespace ui {
+class LocatedEvent;
+class OSExchangeData;
+class Window;
+}
+
+namespace views {
+
+// An aura client object that translates aura dragging methods to their
+// remote ui::Window equivalents.
+class DragDropClientMus : public aura::client::DragDropClient {
+ public:
+  DragDropClientMus(aura::Window* aura_window, ui::Window* ui_window);
+  ~DragDropClientMus() override;
+
+  // Overridden from aura::client::DragDropClient:
+  int StartDragAndDrop(const ui::OSExchangeData& data,
+                       aura::Window* root_window,
+                       aura::Window* source_window,
+                       const gfx::Point& screen_location,
+                       int drag_operations,
+                       ui::DragDropTypes::DragEventSource source) override;
+  void DragUpdate(aura::Window* target,
+                  const ui::LocatedEvent& event) override;
+  void Drop(aura::Window* target,
+            const ui::LocatedEvent& event) override;
+  void DragCancel() override;
+  bool IsDragDropInProgress() override;
+
+ private:
+  aura::Window* aura_window_;
+  ui::Window* ui_window_;
+
+  DISALLOW_COPY_AND_ASSIGN(DragDropClientMus);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_MUS_DRAG_DROP_CLIENT_MUS_H_