Move GrGLInterface function pointers into a nested struct

include/gpu/gl/GrGLExtensions.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrGLExtensions_DEFINED
 #define GrGLExtensions_DEFINED
 
 #include "GrGLFunctions.h"
 #include "SkString.h"
 #include "SkTArray.h"
 
 struct GrGLInterface;
 
 /**
  * This helper queries the current GL context for its extensions, remembers them, and can be
  * queried. It supports both glGetString- and glGetStringi-style extension string APIs and will
  * use the latter if it is available.
  */
 class GrGLExtensions : public SkNoncopyable {
 public:
-
     GrGLExtensions() : fInitialized(false), fStrings(SkNEW(SkTArray<SkString>)) {}
 
     void swap(GrGLExtensions* that) {
         fStrings.swap(&that->fStrings);
     }
 
     /**
      * We sometimes need to use this class without having yet created a GrGLInterface. This version
      * of init expects that getString is always non-NULL while getIntegerv and getStringi are non-
      * NULL if on desktop GL with version 3.0 or higher. Otherwise it will fail.
@@ skipping 13 matching lines @@
     void reset() { fStrings->reset(); }
 
     void print(const char* sep = "\n") const;
 
 private:
     bool                                fInitialized;
     SkAutoTDelete<SkTArray<SkString> >  fStrings;
 };
 
 #endif