mus: Use the new drag API to implement tab dragging in chrome.

ui/views/mus/native_widget_mus.h

 // 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.
 
 #ifndef UI_VIEWS_MUS_NATIVE_WIDGET_MUS_H_
 #define UI_VIEWS_MUS_NATIVE_WIDGET_MUS_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 246 matching lines @@
   const mus::mojom::SurfaceType surface_type_;
   mus::mojom::ShowState show_state_before_fullscreen_;
 
   // See class documentation for Widget in widget.h for a note about ownership.
   Widget::InitParams::Ownership ownership_;
 
   // Functions with the same name require the mus::WindowObserver to be in
   // a separate class.
   std::unique_ptr<MusWindowObserver> mus_window_observer_;
 
+  // This is misnamed; The native widget interface offers something called
+  // "native window properties" which are properties which it stores locally,
+  // and this is used to unsafely pass void* pointers around chrome.
+  std::map<std::string, void*> native_window_properties_;
+
   // Aura configuration.
   std::unique_ptr<SurfaceContextFactory> context_factory_;
   std::unique_ptr<WindowTreeHostMus> window_tree_host_;
   aura::Window* content_;
   std::unique_ptr<wm::FocusController> focus_client_;
   std::unique_ptr<MusCaptureClient> capture_client_;
   std::unique_ptr<aura::client::WindowTreeClient> window_tree_client_;
   std::unique_ptr<aura::client::ScreenPositionClient> screen_position_client_;
   std::unique_ptr<wm::CursorManager> cursor_manager_;
 
   // Bitmap management.
   std::unique_ptr<bitmap_uploader::BitmapUploader> bitmap_uploader_;
   std::unique_ptr<ui::ViewProp> prop_;
 
   base::WeakPtrFactory<NativeWidgetMus> close_widget_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(NativeWidgetMus);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_MUS_NATIVE_WIDGET_MUS_H_