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

content/public/browser/web_contents.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 CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_
 
 #include <set>
 
 #include "base/basictypes.h"
@@ skipping 321 matching lines @@
   // change.
   virtual void NotifyNavigationStateChanged(InvalidateTypes changed_flags) = 0;
 
   // Get the last time that the WebContents was made active (either when it was
   // created or shown with WasShown()).
   virtual base::TimeTicks GetLastActiveTime() const = 0;
 
   // Invoked when the WebContents becomes shown/hidden.
   virtual void WasShown() = 0;
   virtual void WasHidden() = 0;
+  virtual void WasHidden(bool content_visible) = 0;
 
   // Returns true if the before unload and unload listeners need to be
   // fired. The value of this changes over time. For example, if true and the
   // before unload listener is executed and allows the user to exit, then this
   // returns false.
   virtual bool NeedToFireBeforeUnload() = 0;
 
   // Runs the beforeunload handler for the main frame. See also ClosePage and
   // SwapOut in RenderViewHost, which run the unload handler.
   //
@@ skipping 266 matching lines @@
 
  private:
   // This interface should only be implemented inside content.
   friend class WebContentsImpl;
   WebContents() {}
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_H_