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

ui/wm/core/focus_controller.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_WM_CORE_FOCUS_CONTROLLER_H_
 #define UI_WM_CORE_FOCUS_CONTROLLER_H_
 
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
@@ skipping 52 matching lines @@
   aura::Window* GetFocusedWindow() override;
 
   // Overridden from ui::EventHandler:
   void OnKeyEvent(ui::KeyEvent* event) override;
   void OnMouseEvent(ui::MouseEvent* event) override;
   void OnScrollEvent(ui::ScrollEvent* event) override;
   void OnTouchEvent(ui::TouchEvent* event) override;
   void OnGestureEvent(ui::GestureEvent* event) override;
 
   // Overridden from aura::WindowObserver:
-  void OnWindowVisibilityChanged(aura::Window* window, bool visible) override;
+  void OnWindowVisibilityChanged(aura::Window* window, bool visible,
+                                 bool contentVisible) override;

[Elliot Glaysher, 2015/03/03 00:33:52]

nit: camel case doesn't match the cc file, use unix_hacker for variable names. 

   void OnWindowDestroying(aura::Window* window) override;
   void OnWindowHierarchyChanging(const HierarchyChangeParams& params) override;
   void OnWindowHierarchyChanged(const HierarchyChangeParams& params) override;
 
   // Internal implementation that sets the focused window, fires events etc.
   // This function must be called with a valid focusable window.
   void SetFocusedWindow(aura::Window* window);
 
   // Internal implementation that sets the active window, fires events etc.
   // This function must be called with a valid |activatable_window|.
@@ skipping 27 matching lines @@
   ObserverList<aura::client::FocusChangeObserver> focus_observers_;
 
   ScopedObserver<aura::Window, aura::WindowObserver> observer_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(FocusController);
 };
 
 }  // namespace wm
 
 #endif  // UI_WM_CORE_FOCUS_CONTROLLER_H_