Fixes lack of forward declaration of GdkEvent in render_widget_host_view

content/public/browser/render_widget_host_view.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_VIEW_H_
 #define CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_VIEW_H_
 #pragma once
 
 #if defined(TOOLKIT_GTK)
 #include <gdk/gdk.h>
 #endif
 
 #include "content/common/content_export.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebInputEvent.h"
 #include "ui/gfx/native_widget_types.h"
 
+#if defined(TOOLKIT_GTK)
+class GdkEventButton;
+#endif
+
 class BrowserAccessibilityManager;
 
 namespace gfx {
 class Rect;
 class Size;
 }
 
 namespace content {
 
 class RenderWidgetHost;
@@ skipping 113 matching lines @@
   // Return value indicates whether the mouse is locked successfully or not.
   virtual bool LockMouse() = 0;
   virtual void UnlockMouse() = 0;
   // Returns true if the mouse pointer is currently locked.
   virtual bool IsMouseLocked() = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_VIEW_H_