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

ash/wm/maximize_mode/workspace_backdrop_delegate.h

Index: ash/wm/maximize_mode/workspace_backdrop_delegate.h
diff --git a/ash/wm/maximize_mode/workspace_backdrop_delegate.h b/ash/wm/maximize_mode/workspace_backdrop_delegate.h
new file mode 100644
index 0000000000000000000000000000000000000000..2a9ab2d51e2916f2924a68504b1e0ad2f2b4bdb3
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+++ b/ash/wm/maximize_mode/workspace_backdrop_delegate.h
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+// Copyright (c) 2014 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_WM_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_
+#define ASH_WM_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_
+
+#include "ash/wm/workspace/workspace_layout_manager_delegate.h"
+#include "ui/aura/window_observer.h"
+
+namespace aura {
+class Window;
+}
+
+namespace ui {
+class Layer;
+}
+
+namespace views {
+class Widget;
+}
+
+namespace ash {
+
+namespace internal {
+
+// A background which gets created for a container |window| and which gets
+// stacked behind the topmost window (within that container) covering the
+// entire container.
+class WorkspaceBackdropDelegate : public aura::WindowObserver,
+                                  public WorkspaceLayoutManagerDelegate {
+ public:
+  explicit WorkspaceBackdropDelegate(aura::Window* container);
+  virtual ~WorkspaceBackdropDelegate();
+
+  // WindowObserver overrides:
+  virtual void OnWindowBoundsChanged(aura::Window* window,
+                                     const gfx::Rect& old_bounds,
+                                     const gfx::Rect& new_bounds) OVERRIDE;
+
+  // WorkspaceLayoutManagerDelegate overrides:
+  virtual void OnWindowAddedToLayout(aura::Window* child);
+  virtual void OnWindowRemovedFromLayout(aura::Window* child);
+  virtual void OnChildWindowVisibilityChanged(aura::Window* child,
+                                              bool visible);
+  virtual void OnWindowStackingChanged(aura::Window* window);
+  virtual void OnPostWindowStateTypeChange(wm::WindowState* window_state,
+                                           wm::WindowStateType old_type);
+
+ private:
+  // Restack the backdrop relatively to the other windows in the container.
+  void RestackBackdrop();
+
+  // Returns the current visible top level window in the container.
+  aura::Window* GetCurrentTopWindow();
+
+  // Position & size the background over the container window.
+  void AdjustToContainerBounds();
+
+  // Show the overlay.
+  void Show();
+
+  // The background which covers the rest of the screen.
+  views::Widget* background_;
+
+  // The window which is being "maximized".
+  aura::Window* container_;
+
+  // If true, the |RestackOrHideWindow| might recurse.
+  bool in_restacking_;
+
+  DISALLOW_COPY_AND_ASSIGN(WorkspaceBackdropDelegate);
+};
+
+}  // namespace internal
+
+}  // namespace ash
+
+#endif  // ASH_WM_MAXIMIZE_MODE_WORKSPACE_BACKDROP_DELEGATE_H_