WorkspaceLayoutManager backdrop should fill entire region.

ash/wm/workspace/workspace_layout_manager_delegate.h

 // 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_LAYOUT_MANAGER_DELEGATE_H_
 #define ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_DELEGATE_H_
 
 #include "ash/wm/wm_types.h"
 
 namespace aura {
@@ skipping 21 matching lines @@
   // The visibility of a window has changed.
   virtual void OnChildWindowVisibilityChanged(aura::Window* child,
                                               bool visible) = 0;
 
   // The stacking order of a window has changed.
   virtual void OnWindowStackingChanged(aura::Window* window) = 0;
 
   // A window state type has changed.
   virtual void OnPostWindowStateTypeChange(wm::WindowState* window_state,
                                            wm::WindowStateType old_type) = 0;
+
+  // The work area insets have changed, altering the total available space.
+  virtual void OnDisplayWorkAreaInsetsChanged() = 0;
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_WORKSPACE_WORKSPACE_LAYOUT_MANAGER_DELEGATE_H_