Make null GL context use callback to make current

include/gpu/gl/SkNullGLContext.h

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkNullGLContext_DEFINED
 #define SkNullGLContext_DEFINED
 
 #include "gl/SkGLContext.h"
 
 class SK_API SkNullGLContext : public SkGLContext {
 public:
     ~SkNullGLContext() SK_OVERRIDE;
     void makeCurrent() const SK_OVERRIDE;
     void swapBuffers() const SK_OVERRIDE {};
 
     static SkNullGLContext* Create(GrGLStandard);
 
-    struct ContextState;
+    class ContextState;
 
 private:
     SkNullGLContext();
 
     ContextState* fState;
 };
 
 #endif