Add SkSpecialImage::extractSubset & NewFromPixmap

tests/TestingSpecialImageAccess.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file
  */
 
 #ifndef TestingSpecialImageAccess_DEFINED
 #define TestingSpecialImageAccess_DEFINED
 
 class TestingSpecialImageAccess {
 public:
     static const SkIRect& Subset(const SkSpecialImage* img) {
         return img->subset();
     }
 
     static bool PeekPixels(const SkSpecialImage* img, SkPixmap* pixmap) {
-        return img->testingOnlyPeekPixels(pixmap);
+        return img->peekPixels(pixmap);
     }
 
     static GrTexture* PeekTexture(const SkSpecialImage* img) {
         return img->peekTexture();
     }
 
     static bool GetROPixels(const SkSpecialImage* img, SkBitmap* result) {
         return img->testingOnlyGetROPixels(result);
     }
 };
 
 #endif