When a surface is backed by an external render target force a copy on image snap

tests/SurfaceTest.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <functional>
 #include "SkCanvas.h"
 #include "SkData.h"
@@ skipping 421 matching lines @@
         GrBackendTextureDesc desc;
         desc.fConfig = kRGBA_8888_GrPixelConfig;
         desc.fWidth = 10;
         desc.fHeight = 10;
         desc.fFlags = kRenderTarget_GrBackendTextureFlag;
         desc.fTextureHandle = textureObject;
         GrTexture* texture = context->textureProvider()->wrapBackendTexture(desc);
         {
             SkAutoTUnref<SkSurface> surface(
                 SkSurface::NewRenderTargetDirect(texture->asRenderTarget()));
-            // We should be able to pass true here, but disallowing copy on write for direct GPU
-            // surfaces is not yet implemented.
-            test_unique_image_snap(reporter, surface, false, imageBackingStore,
+            test_unique_image_snap(reporter, surface, true, imageBackingStore,
                                    surfaceBackingStore);
         }
         texture->unref();
         context->getGpu()->deleteTestingOnlyBackendTexture(textureObject);
     }
 }
 #endif
 
 #if SK_SUPPORT_GPU
 // May we (soon) eliminate the need to keep testing this, by hiding the bloody device!
@@ skipping 451 matching lines @@
         desc.fHeight = kHeight;
         desc.fFlags = kRenderTarget_GrBackendTextureFlag;
         desc.fTextureHandle = textureObject;
 
         SkSurface* surface = SkSurface::NewFromBackendTexture(context, desc, nullptr);
         test_surface_clear(reporter, surface, grSurfaceGetter, 0xABABABAB);
         context->getGpu()->deleteTestingOnlyBackendTexture(textureObject);
     }
 }
 #endif