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

ui/wm/core/transient_window_manager.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 UI_WM_CORE_TRANSIENT_WINDOW_MANAGER_H_
 #define UI_WM_CORE_TRANSIENT_WINDOW_MANAGER_H_
 
 #include <vector>
 
 #include "base/observer_list.h"
@@ skipping 64 matching lines @@
   // above it.
   void RestackTransientDescendants();
 
   // Update the window's visibility following the transient parent's
   // visibility. See |set_parent_controls_visibility(bool)| for more details.
   void UpdateTransientChildVisibility(bool visible);
 
   // WindowObserver:
   void OnWindowParentChanged(aura::Window* window,
                              aura::Window* parent) override;
-  void OnWindowVisibilityChanged(aura::Window* window, bool visible) override;
+  void OnWindowVisibilityChanged(aura::Window* window, bool visible,
+                                 bool content_visible) override;
   void OnWindowStackingChanged(aura::Window* window) override;
   void OnWindowDestroying(aura::Window* window) override;
 
   aura::Window* window_;
   aura::Window* transient_parent_;
   Windows transient_children_;
 
   // If non-null we're actively restacking transient as the result of a
   // transient ancestor changing.
   aura::Window* stacking_target_;
 
   bool parent_controls_visibility_;
   bool show_on_parent_visible_;
   bool ignore_visibility_changed_event_;
 
   ObserverList<TransientWindowObserver> observers_;
 
   DISALLOW_COPY_AND_ASSIGN(TransientWindowManager);
 };
 
 }  // namespace wm
 
 #endif  // UI_WM_CORE_TRANSIENT_WINDOW_MANAGER_H_