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

content/browser/renderer_host/render_widget_host_view_base.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_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_BASE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_BASE_H_
 
 #if defined(OS_MACOSX)
 #include <OpenGL/OpenGL.h>
 #endif
@@ skipping 61 matching lines @@
   void WasOccluded() override {}
   bool IsShowingContextMenu() const override;
   void SetShowingContextMenu(bool showing_menu) override;
   base::string16 GetSelectedText() const override;
   bool IsMouseLocked() override;
   gfx::Size GetVisibleViewportSize() const override;
   void SetInsets(const gfx::Insets& insets) override;
   void BeginFrameSubscription(
       scoped_ptr<RenderWidgetHostViewFrameSubscriber> subscriber) override;
   void EndFrameSubscription() override;
+  void SetWindowVisibility(bool visible) override {}
 
   // IPC::Listener implementation:
   bool OnMessageReceived(const IPC::Message& msg) override;
 
   void SetPopupType(blink::WebPopupType popup_type);
 
   blink::WebPopupType GetPopupType();
 
   // Return a value that is incremented each time the renderer swaps a new frame
   // to the view.
@@ skipping 328 matching lines @@
   base::OneShotTimer<RenderWidgetHostViewBase> flush_input_timer_;
 
   base::WeakPtrFactory<RenderWidgetHostViewBase> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewBase);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_BASE_H_