Add swapBuffer call to SkGLContextHelper.

src/gpu/gl/iOS/SkNativeGLContext_iOS.mm

 
 /*
  * 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/SkNativeGLContext.h"
 #import <OpenGLES/EAGL.h>
@@ skipping 42 matching lines @@
         return NULL;
     }
     return interface;
 }
 
 void SkNativeGLContext::makeCurrent() const {
     if (![EAGLContext setCurrentContext:EAGLCTX]) {
         SkDebugf("Could not set the context.\n");
     }
 }
+
+void SkNativeGLContext::swapBuffers() const { }