Adding a gray semi transparent backdrop behind the topmost window within the default container

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 273 matching lines @@
   // Called when the application is exiting.
   void OnAppTerminating();
 
   // Called when the screen is locked (after the lock window is visible) or
   // unlocked.
   void OnLockStateChanged(bool locked);
 
   // Called when a casting session is started or stopped.
   void OnCastingSessionStartedOrStopped(bool started);
 
+  // Called when the overview mode has started.
+  void OnOverviewModeStarted();
+
+  // Called when the overview mode has ended.
+  void OnOverviewModeEnded();
+
   // Initializes |shelf_|.  Does nothing if it's already initialized.
   void CreateShelf();
 
   // Creates a virtual keyboard. Deletes the old virtual keyboard if it already
   // exists.
   void CreateKeyboard();
 
   // Deactivates the virtual keyboard.
   void DeactivateKeyboard();
 
   // Show shelf view if it was created hidden (before session has started).
   void ShowShelf();
 
   // Adds/removes observer.
   void AddShellObserver(ShellObserver* observer);
   void RemoveShellObserver(ShellObserver* observer);
 
   // Turn the always maximize mode window manager on or off.
   void EnableMaximizeModeWindowManager(bool enable);
 
+  // Test if the MaximizeModeWindowManager is enabled or not.
+  bool IsMaximizeModeWindowManagerEnabled();
+
   keyboard::KeyboardController* keyboard_controller() {
     return keyboard_controller_.get();
   }
 
   AcceleratorController* accelerator_controller() {
     return accelerator_controller_.get();
   }
 
   internal::DisplayManager* display_manager() {
     return display_manager_.get();
@@ skipping 401 matching lines @@
 
   // Injected content::GPUDataManager support.
   scoped_ptr<GPUSupport> gpu_support_;
 
   DISALLOW_COPY_AND_ASSIGN(Shell);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELL_H_