Refactor SkGLContext to be actually extendable

src/gpu/gl/SkNullGLContext.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gl/SkNullGLContext.h"
 
-const GrGLInterface* SkNullGLContext::createGLContext(GrGLStandard forcedGpuAPI) {
-    if (kGLES_GrGLStandard == forcedGpuAPI) {
-        return NULL;
-    }
-    return GrGLCreateNullInterface();
-};
+SkNullGLContext::SkNullGLContext() {
+    fGL.reset(GrGLCreateNullInterface());
+}
+
+SkNullGLContext::~SkNullGLContext() {
+    fGL.reset(NULL);
+}
+