Refactor backdrop that is currently used in the maximized mode.

ash/wm/workspace/backdrop_controller.h

Index: ash/wm/workspace/backdrop_controller.h
diff --git a/ash/wm/workspace/backdrop_controller.h b/ash/wm/workspace/backdrop_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..6bc576b926290865a0965c95ab9d151901d40e5f
--- /dev/null
+++ b/ash/wm/workspace/backdrop_controller.h
@@ -0,0 +1,116 @@
+// Copyright 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_WORKSPACE_WORKSPACE_BACKDROP_DELEGATE_IMPL_H_
+#define ASH_WM_WORKSPACE_WORKSPACE_BACKDROP_DELEGATE_IMPL_H_
+
+#include <memory>
+
+#include "ash/shell_observer.h"
+#include "ash/system/accessibility_observer.h"
+#include "ash/wm/wm_types.h"
+#include "base/macros.h"
+
+namespace aura {
+class Window;
+}
+
+namespace views {
+class Widget;
+}
+
+namespace ui {
+class EventHandler;
+}
+
+namespace ash {
+namespace test {
+class WorkspaceControllerTestApi;
+}
+
+namespace wm {
+class WindowState;
+}
+
+class BackdropDelegate;
+
+// A backdrop which gets created for a container |window| and which gets
+// stacked behind the top level, activatable window that meets the following
+// criteria.
+//
+// 1) Has a aura::client::kHasBackdrop property = true.
+// 2) BackdropDelegate::HasBackdrop(aura::Window* window) returns true.
+// 3) Active ARC window when the spoken feedback is enabled.
+class BackdropController : public ShellObserver, public AccessibilityObserver {
+ public:
+  explicit BackdropController(aura::Window* container);
+  ~BackdropController() override;
+
+  void OnWindowAddedToLayout(aura::Window* child);
+  void OnWindowRemovedFromLayout(aura::Window* child);
+  void OnChildWindowVisibilityChanged(aura::Window* child, bool visible);
+  void OnWindowStackingChanged(aura::Window* window);
+  void OnPostWindowStateTypeChange(wm::WindowState* window_state,
+                                   wm::WindowStateType old_type);
+
+  void SetBackdropDelegate(std::unique_ptr<BackdropDelegate> delegate);
+
+  // Update the visibility of, and restack the backdrop relative to
+  // the other windows in the container.
+  void UpdateBackdrop();
+
+  // ShellObserver:
+  void OnOverviewModeStarting() override;
+  void OnOverviewModeEnded() override;
+
+  // AccessibilityObserver:
+  void OnAccessibilityModeChanged(
+      AccessibilityNotificationVisibility notify) override;
+
+ private:
+  friend class test::WorkspaceControllerTestApi;
+
+  void EnsureBackdropWidget();
+
+  void UpdateAccessibilityMode();
+
+  // Returns the current visible top level window in the container.
+  aura::Window* GetTopmostWindowWithBackdrop();
+
+  bool WindowShouldHaveBackdrop(aura::Window* window);
+
+  // Show the backdrop window.
+  void Show();
+
+  // Hide the backdrop window.
+  void Hide();
+
+  // The backdrop which covers the rest of the screen.
+  views::Widget* backdrop_ = nullptr;
+
+  // aura::Window for |backdrop_|.
+  aura::Window* backdrop_window_ = nullptr;
+
+  // The container of the window that should have a backdrop.
+  aura::Window* container_;
+
+  std::unique_ptr<BackdropDelegate> delegate_;
+
+  // Event hanlder used to implement actions for accessibility.
+  std::unique_ptr<ui::EventHandler> backdrop_event_handler_;
+  ui::EventHandler* original_event_handler_ = nullptr;
+
+  // If true, the |RestackOrHideWindow| might recurse.
+  bool in_restacking_ = false;
+
+  // True to temporarily hide the backdrop. Used in
+  // overview mode.
+  bool force_hidden_ = false;
+
+  DISALLOW_COPY_AND_ASSIGN(BackdropController);
+};
+
+}  // namespace ash
+
+#endif  // ASH_WM_WORKSPACE_WORKSPACE_BACKDROP_DELEGATE_IMPL_H_