Add context to gfx::Screen calls in support of simultaneous desktop+ash

ash/shell.h

 // Copyright (c) 2012 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 ASH_SHELL_H_
 #define ASH_SHELL_H_
 
 #include <utility>
 #include <vector>
 
@@ skipping 149 matching lines @@
   // Returns the primary RootWindow. The primary RootWindow is the one
   // that has a launcher.
   static aura::RootWindow* GetPrimaryRootWindow();
 
   // Returns the active RootWindow. The active RootWindow is the one that
   // contains the current active window as a decendant child. The active
   // RootWindow remains the same even when the active window becomes NULL,
   // until the another window who has a different root window becomes active.
   static aura::RootWindow* GetActiveRootWindow();
 
+  // Returns the active RootWindow as a NativeView.
+  static gfx::NativeView GetRootNativeView();
+
   // Returns all root windows.
   static RootWindowList GetAllRootWindows();
 
   static aura::Window* GetContainer(aura::RootWindow* root_window,
                                     int container_id);
 
   // Returns the list of containers that match |container_id| in
   // all root windows.
   static std::vector<aura::Window*> GetAllContainers(int container_id);
 
@@ skipping 308 matching lines @@
 
   // Used by ash/shell.
   content::BrowserContext* browser_context_;
 
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELL_H_