Clean forward declaration in public

Source/web/WebViewImpl.h

 /*
  * Copyright (C) 2010 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 54 matching lines @@
 
 class DataObject;
 class Frame;
 class FullscreenController;
 class LinkHighlight;
 class PopupContainer;
 class RenderLayerCompositor;
 class UserGestureToken;
 class WebActiveGestureAnimation;
 class WebDevToolsAgentPrivate;
+class WebLayerTreeView;
 class WebLocalFrameImpl;
 class WebImage;
 class WebPagePopupImpl;
 class WebPlugin;
 class WebSettingsImpl;
 
 struct WebSelectionBound;
 
 class WebViewImpl final : public WebView
     , public RefCounted<WebViewImpl>
@@ skipping 666 matching lines @@
     float m_topControlsLayoutHeight;
 };
 
 // We have no ways to check if the specified WebView is an instance of
 // WebViewImpl because WebViewImpl is the only implementation of WebView.
 DEFINE_TYPE_CASTS(WebViewImpl, WebView, webView, true, true);
 
 } // namespace blink
 
 #endif