remove unused (by the outside) SkImage::newSurface, and simplify newImage -> newSubset

gm/surface.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkGradientShader.h"
 #include "SkSurface.h"
@@ skipping 125 matching lines @@
 
         SkAutoTUnref<SkSurface> surf(canvas->newSurface(info, nullptr));
         if (!surf.get()) {
             surf.reset(SkSurface::NewRaster(info));
         }
         drawInto(surf->getCanvas());
 
         SkAutoTUnref<SkImage> image(surf->newImageSnapshot());
         canvas->drawImage(image, 10, 10, nullptr);
 
-        SkAutoTUnref<SkSurface> surf2(image->newSurface(info, nullptr));
+        SkAutoTUnref<SkSurface> surf2(surf->newSurface(info));
         drawInto(surf2->getCanvas());
 
         // Assert that the props were communicated transitively through the first image
         SkASSERT(equal(surf->props(), surf2->props()));
 
         SkAutoTUnref<SkImage> image2(surf2->newImageSnapshot());
         canvas->drawImage(image2, 10 + SkIntToScalar(image->width()) + 10, 10, nullptr);
     }
 
 private:
     typedef GM INHERITED;
 };
 DEF_GM( return new NewSurfaceGM )