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

ash/wm/workspace_controller.cc

 // 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.
 
 #include "ash/wm/workspace_controller.h"
 
 #include "ash/root_window_controller.h"
 #include "ash/shelf/shelf_layout_manager.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ skipping 117 matching lines @@
             ui::LayerAnimationElement::BRIGHTNESS |
             ui::LayerAnimationElement::VISIBILITY);
     settings.SetTweenType(gfx::Tween::EASE_OUT);
     settings.SetTransitionDuration(
         base::TimeDelta::FromMilliseconds(kCrossFadeDurationMS));
     viewport_->layer()->SetTransform(gfx::Transform());
     viewport_->layer()->SetOpacity(1.0f);
   }
 }
 
+void WorkspaceController::AddBackdropBehindTopWindow(bool enable) {
+  layout_manager_->AddBackdropBehindTopWindow(enable);
+}
+
 }  // namespace internal
 }  // namespace ash