Don't copy image buffer when calculating size.

src/image/SkImage_Gpu.h

Index: src/image/SkImage_Gpu.h
diff --git a/src/image/SkImage_Gpu.h b/src/image/SkImage_Gpu.h
index 13c1e306dc93b95b66ac4611733a90371354f547..76d8a7f6437f1403c0e3a7e4f273e007704ffc17 100644
--- a/src/image/SkImage_Gpu.h
+++ b/src/image/SkImage_Gpu.h
@@ -50,6 +50,18 @@ public:
     }
     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;