Refactor backdrop that is currently used in the maximized mode.

ash/wm/workspace/backdrop_delegate.h

Index: ash/wm/workspace/backdrop_delegate.h
diff --git a/ash/wm/workspace/workspace_layout_manager_backdrop_delegate.h b/ash/wm/workspace/backdrop_delegate.h
similarity index 42%
rename from ash/wm/workspace/workspace_layout_manager_backdrop_delegate.h
rename to ash/wm/workspace/backdrop_delegate.h
index 4eaf81b80566f649954f0776f9574589ae674b59..6a7dca161a83855813d15562f7ed0b877ff8fa82 100644
--- a/ash/wm/workspace/workspace_layout_manager_backdrop_delegate.h
+++ b/ash/wm/workspace/backdrop_delegate.h
@@ -6,38 +6,21 @@
 #define ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_BACKDROP_DELEGATE_H_
 
 #include "ash/ash_export.h"
-#include "ash/wm/wm_types.h"
 
-namespace ash {
-
-class WmWindow;
-
-namespace wm {
-class WindowState;
+namespace aura {
+class Window;
 }
 
+namespace ash {
+
 // A delegate which can be set to create and control a backdrop which gets
 // placed below the top level window.
-class ASH_EXPORT WorkspaceLayoutManagerBackdropDelegate {
+class ASH_EXPORT BackdropDelegate {
  public:
-  virtual ~WorkspaceLayoutManagerBackdropDelegate() {}
+  virtual ~BackdropDelegate() {}
 
   // A window got added to the layout.
-  virtual void OnWindowAddedToLayout(WmWindow* child) = 0;
-
-  // A window got removed from the layout.
-  virtual void OnWindowRemovedFromLayout(WmWindow* child) = 0;
-
-  // The visibility of a window has changed.
-  virtual void OnChildWindowVisibilityChanged(WmWindow* child,
-                                              bool visible) = 0;
-
-  // The stacking order of a window has changed.
-  virtual void OnWindowStackingChanged(WmWindow* window) = 0;
-
-  // A window state type has changed.
-  virtual void OnPostWindowStateTypeChange(wm::WindowState* window_state,
-                                           wm::WindowStateType old_type) = 0;
+  virtual bool HasBackdrop(aura::Window* window) = 0;
 };
 
 }  // namespace ash