Add setVisibilityState API to WebFrameWidget

public/web/WebFrameWidget.h

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 14 matching lines @@
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef WebFrameWidget_h
 #define WebFrameWidget_h
 
 #include "../platform/WebCommon.h"
+#include "../platform/WebPageVisibilityState.h"
 #include "public/web/WebWidget.h"
 
 namespace blink {
 
 class WebLocalFrame;
 class WebWidgetClient;
 
 class WebFrameWidget : public WebWidget {
 public:
     BLINK_EXPORT static WebFrameWidget* create(WebWidgetClient*, WebLocalFrame*);
+
+    // We still track page-level visibility, but additionally we need to notify a WebFrameWidget
+    // when its owning RenderWidget receives a Show or Hide directive, so that it knows whether
+    // it needs to draw or not.
+    virtual void setVisibilityState(WebPageVisibilityState visibilityState, bool isInitialState) { }
 };
 
 } // namespace blink
 
 #endif