Implement SkGLContext swapBuffers with fence syncs

src/gpu/gl/debug/SkDebugGLContext.cpp

 
 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gl/debug/SkDebugGLContext.h"
 
 SkDebugGLContext::SkDebugGLContext() {
-    fGL.reset(GrGLCreateDebugInterface());
+    this->init(GrGLCreateDebugInterface());
 }
 
 SkDebugGLContext::~SkDebugGLContext() {
-    fGL.reset(NULL);
+    this->teardown();
 }