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

ui/views/mus/window_manager_connection.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_WINDOW_MANAGER_CONNECTION_H_
 #define UI_VIEWS_MUS_WINDOW_MANAGER_CONNECTION_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 49 matching lines @@
                          std::vector<uint8_t>>& properties);
 
   NativeWidget* CreateNativeWidgetMus(
       const std::map<std::string, std::vector<uint8_t>>& properties,
       const Widget::InitParams& init_params,
       internal::NativeWidgetDelegate* delegate);
 
   void AddPointerWatcher(PointerWatcher* watcher);
   void RemovePointerWatcher(PointerWatcher* watcher);
 
+  const std::set<mus::Window*>& GetRoots() const;
+
  private:
   friend class WindowManagerConnectionTest;
 
   WindowManagerConnection(shell::Connector* connector,
                           const shell::Identity& identity);
 
   // Returns true if there is one or more pointer watchers for this client.
   bool HasPointerWatcher();
 
   // mus::WindowTreeClientDelegate:
@@ skipping 11 matching lines @@
   std::unique_ptr<mus::WindowTreeClient> client_;
   // Must be empty on destruction.
   base::ObserverList<PointerWatcher, true> pointer_watchers_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowManagerConnection);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_MUS_WINDOW_MANAGER_CONNECTION_H_