Revert of Make the Sk GL context class an abstract base class

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 "SkGLContext.h"
+#include "SkGLContextHelper.h"
 
-class SK_API SkNullGLContext : public SkGLContext {
+class SK_API SkNullGLContext : public SkGLContextHelper {
 
 public:
     SkNullGLContext() {};
 
     virtual void makeCurrent() const SK_OVERRIDE {};
 
     virtual void swapBuffers() const SK_OVERRIDE {};
 
 protected:
     virtual const GrGLInterface* createGLContext(GrGLStandard forcedGpuAPI) SK_OVERRIDE;
 
     virtual void destroyGLContext() SK_OVERRIDE {};
 };
 
 #endif