ui: Cleanup class/struct forward declarations

ui/gl/gl_osmesa_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_OSMESA_API_IMPLEMENTATION_H_
 #define UI_GL_GL_OSMESA_API_IMPLEMENTATION_H_
 
 #include "base/compiler_specific.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_export.h"
 
 namespace gl {
 
-class GLContext;
-
 GL_EXPORT void InitializeStaticGLBindingsOSMESA();
 GL_EXPORT void InitializeDebugGLBindingsOSMESA();
 GL_EXPORT void ClearGLBindingsOSMESA();
 
 class GL_EXPORT OSMESAApiBase : public OSMESAApi {
  public:
   // Include the auto-generated part of this class. We split this because
   // it means we can easily edit the non-auto generated parts right here in
   // this file instead of having to edit some template or the code generator.
   #include "gl_bindings_api_autogen_osmesa.h"
@@ skipping 27 matching lines @@
  private:
   OSMESAApi* osmesa_api_;
 };
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_OSMESA_API_IMPLEMENTATION_H_