Make Page Visibility API work when the browser window is visible or not

ui/aura/window_observer.h

 // Copyright (c) 2012 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 UI_AURA_WINDOW_OBSERVER_H_
 #define UI_AURA_WINDOW_OBSERVER_H_
 
 #include "base/basictypes.h"
 #include "base/strings/string16.h"
 #include "ui/aura/aura_export.h"
@@ skipping 52 matching lines @@
   // compared for equality with the property constant. |old| is the old property
   // value, which must be cast to the appropriate type before use.
   virtual void OnWindowPropertyChanged(Window* window,
                                        const void* key,
                                        intptr_t old) {}
 
   // Invoked when SetVisible() is invoked on a window. |visible| is the
   // value supplied to SetVisible(). If |visible| is true, window->IsVisible()
   // may still return false. See description in Window::IsVisible() for details.
   virtual void OnWindowVisibilityChanging(Window* window, bool visible) {}
-  virtual void OnWindowVisibilityChanged(Window* window, bool visible) {}
+  virtual void OnWindowVisibilityChanged(Window* window, bool visible,
+                                         bool content_visible) {}
 
   // Invoked when SetBounds() is invoked on |window|. |old_bounds| and
   // |new_bounds| are in parent coordinates.
   virtual void OnWindowBoundsChanged(Window* window,
                                      const gfx::Rect& old_bounds,
                                      const gfx::Rect& new_bounds) {}
 
   // Invoked when SetTransform() is invoked on |window|.
   virtual void OnWindowTransforming(Window* window) {}
   virtual void OnWindowTransformed(Window* window) {}
@@ skipping 51 matching lines @@
   // Tracks the number of windows being observed to track down
   // http://crbug.com/365364.
   int observing_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowObserver);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_OBSERVER_H_