Clean up forward declarations in Source/web

Source/web/WebPluginContainerImpl.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2014 Opera Software ASA. 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.
@@ skipping 33 matching lines @@
 
 struct NPObject;
 
 namespace blink {
 
 class GestureEvent;
 class HTMLPlugInElement;
 class IntRect;
 class KeyboardEvent;
 class MouseEvent;
-class PlatformGestureEvent;
 class ResourceError;
 class ResourceResponse;
-class ScriptController;
 class ScrollbarGroup;
 class TouchEvent;
 class WebPlugin;
 class WebPluginLoadObserver;
-class WebExternalTextureLayer;
 class WheelEvent;
 class Widget;
 struct WebPrintParams;
 
 class WebPluginContainerImpl final : public PluginView, public WebPluginContainer, public FrameDestructionObserver {
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(WebPluginContainerImpl);
 public:
     static PassRefPtrWillBeRawPtr<WebPluginContainerImpl> create(HTMLPlugInElement* element, WebPlugin* webPlugin)
     {
         return adoptRefWillBeNoop(new WebPluginContainerImpl(element, webPlugin));
@@ skipping 146 matching lines @@
 };
 
 DEFINE_TYPE_CASTS(WebPluginContainerImpl, Widget, widget, widget->isPluginContainer(), widget.isPluginContainer());
 // Unlike Widget, we need not worry about object type for container.
 // WebPluginContainerImpl is the only subclass of WebPluginContainer.
 DEFINE_TYPE_CASTS(WebPluginContainerImpl, WebPluginContainer, container, true, true);
 
 } // namespace blink
 
 #endif