Don't copy image buffer when calculating size.

src/image/SkImage_Gpu.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImage_Gpu_DEFINED
 #define SkImage_Gpu_DEFINED
 
@@ skipping 32 matching lines @@
                             SkDestinationSurfaceColorMode) const override;
     sk_sp<SkImage> onMakeSubset(const SkIRect&) const override;
 
     GrTexture* peekTexture() const override { return fTexture.get(); }
     sk_sp<GrTexture> refPinnedTexture(uint32_t* uniqueID) const override {
         *uniqueID = this->uniqueID();
         return fTexture;
     }
     bool onReadPixels(const SkImageInfo&, void* dstPixels, size_t dstRowBytes,
                       int srcX, int srcY, CachingHint) const override;
+#if SK_SUPPORT_GPU
+    bool canGenerateTexture(const GrContextThreadSafeProxy& proxy) const override
+    {
+        return false;
+        /*
+        if (fTexture) {
+            return fTexture->getContext()->uniqueID() == proxy.uniqueID();
+        }
+        return false;
+        */
+    }
+#endif
 
 private:
     sk_sp<GrTexture>       fTexture;
     const SkAlphaType      fAlphaType;
     const SkBudgeted       fBudgeted;
     sk_sp<SkColorSpace>    fColorSpace;
     mutable SkAtomic<bool> fAddedRasterVersionToCache;
 
 
     typedef SkImage_Base INHERITED;
 };
 
 #endif