Implement top controls show/hide functionality for main thread scrolling

public/web/WebWidget.h

 /*
  * Copyright (C) 2009 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 19 matching lines @@
 
 #ifndef WebWidget_h
 #define WebWidget_h
 
 #include "../platform/WebCanvas.h"
 #include "../platform/WebCommon.h"
 #include "../platform/WebFloatSize.h"
 #include "../platform/WebPoint.h"
 #include "../platform/WebRect.h"
 #include "../platform/WebSize.h"
+#include "../platform/WebTopControlsState.h"
 #include "WebBeginFrameArgs.h"
 #include "WebCompositionUnderline.h"
 #include "WebTextDirection.h"
 #include "WebTextInputInfo.h"
 
 namespace blink {
 
 class WebCompositeAndReadbackAsyncCallback;
 class WebInputEvent;
 class WebPagePopup;
@@ skipping 218 matching lines @@
     virtual WebColor backgroundColor() const { return 0xFFFFFFFF; /* SK_ColorWHITE */ }
 
     // The currently open page popup, which are calendar and datalist pickers
     // but not the select popup.
     virtual WebPagePopup* pagePopup() const { return 0; }
 
     // Notification about the top controls height.  If the boolean is true, then
     // the embedder shrunk the WebView size by the top controls height.
     virtual void setTopControlsHeight(float height, bool topControlsShrinkLayoutSize) { }
 
+    // Updates top controls constraints and current state. Allows embedder to
+    // control what are valid states for top controls and if it should animate.
+    virtual void updateTopControlsState(WebTopControlsState constraints, WebTopControlsState current, bool animate) { }
+
 protected:
     ~WebWidget() { }
 };
 
 } // namespace blink
 
 #endif