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

ash/wm/workspace_controller.cc

Index: ash/wm/workspace_controller.cc
diff --git a/ash/wm/workspace_controller.cc b/ash/wm/workspace_controller.cc
index 55ccf64fd6b6e768d0fbf4e1cc50d34b5918c3f3..9b9f35e90323e973dc00900f9eb93ed9c3770365 100644
--- a/ash/wm/workspace_controller.cc
+++ b/ash/wm/workspace_controller.cc
@@ -13,6 +13,7 @@
 #include "ash/wm/window_util.h"
 #include "ash/wm/workspace/workspace_event_handler.h"
 #include "ash/wm/workspace/workspace_layout_manager.h"
+#include "ash/wm/workspace/workspace_layout_manager_delegate.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/window.h"
@@ -135,5 +136,10 @@ void WorkspaceController::DoInitialAnimation() {
   }
 }
 
+void WorkspaceController::SetMaximizeBackdropDelegate(
+    scoped_ptr<WorkspaceLayoutManagerDelegate> delegate) {
+  layout_manager_->SetMaximizeBackdropDelegate(delegate.Pass());
+}
+
 }  // namespace internal
 }  // namespace ash