ui: Cleanup class/struct forward declarations

ui/gl/gl_wgl_api_implementation.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 UI_GL_GL_WGL_API_IMPLEMENTATION_H_
 #define UI_GL_GL_WGL_API_IMPLEMENTATION_H_
 
 #include <vector>
 
 #include "base/compiler_specific.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_export.h"
 
 namespace base {
 class CommandLine;
 }
 namespace gl {
 
-class GLContext;
 struct GLWindowSystemBindingInfo;
 
 GL_EXPORT void InitializeStaticGLBindingsWGL();
 GL_EXPORT void InitializeDebugGLBindingsWGL();
 GL_EXPORT void ClearGLBindingsWGL();
 GL_EXPORT bool GetGLWindowSystemBindingInfoWGL(GLWindowSystemBindingInfo* info);
 
 class GL_EXPORT WGLApiBase : public WGLApi {
  public:
   // Include the auto-generated part of this class. We split this because
@@ skipping 40 matching lines @@
  private:
   WGLApi* wgl_api_;
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_WGL_API_IMPLEMENTATION_H_