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

content/browser/renderer_host/render_widget_host_view_aura.h

Index: content/browser/renderer_host/render_widget_host_view_aura.h
diff --git a/content/browser/renderer_host/render_widget_host_view_aura.h b/content/browser/renderer_host/render_widget_host_view_aura.h
index 89bead7ba5d890cf2c78985745ee68f3cef02191..f87d82a247d5da31a0f03e7e2b4d7741e8750fea 100644
--- a/content/browser/renderer_host/render_widget_host_view_aura.h
+++ b/content/browser/renderer_host/render_widget_host_view_aura.h
@@ -158,6 +158,7 @@ class CONTENT_EXPORT RenderWidgetHostViewAura
   void SetBackgroundColor(SkColor color) override;
   gfx::Size GetVisibleViewportSize() const override;
   void SetInsets(const gfx::Insets& insets) override;
+  void SetWindowVisibility(bool visible);
 
   // Overridden from RenderWidgetHostViewBase:
   void InitAsPopup(RenderWidgetHostView* parent_host_view,
@@ -312,6 +313,9 @@ class CONTENT_EXPORT RenderWidgetHostViewAura
   void OnHostMoved(const aura::WindowTreeHost* host,
                    const gfx::Point& new_origin) override;
 
+  void OnHostSetWindowVisibility(const aura::WindowTreeHost* host,
+                                 bool visible);
+
   void OnTextInputStateChanged(const ViewHostMsg_TextInputState_Params& params);
 
 #if defined(OS_WIN)