ui: Cleanup class/struct forward declarations

ui/gl/gl_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_IMPLEMENTATION_H_
 #define UI_GL_GL_IMPLEMENTATION_H_
 
 #include <string>
 #include <vector>
 
 #include "base/files/file_path.h"
 #include "base/native_library.h"
 #include "build/build_config.h"
 #include "ui/gl/gl_export.h"
 #include "ui/gl/gl_switches.h"
 
 namespace gl {
 
-class GLContext;
-
 // The GL implementation currently in use.
 enum GLImplementation {
   kGLImplementationNone,
   kGLImplementationDesktopGL,
   kGLImplementationDesktopGLCoreProfile,
   kGLImplementationOSMesaGL,
   kGLImplementationAppleGL,
   kGLImplementationEGLGLES2,
   kGLImplementationMockGL
 };
@@ skipping 87 matching lines @@
 
 // Helpers to load a library and log error on failure.
 GL_EXPORT base::NativeLibrary LoadLibraryAndPrintError(
     const base::FilePath::CharType* filename);
 GL_EXPORT base::NativeLibrary LoadLibraryAndPrintError(
     const base::FilePath& filename);
 
 }  // namespace gl
 
 #endif  // UI_GL_GL_IMPLEMENTATION_H_