Don't copy image buffer when calculating size.

src/image/SkImage_Generator.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImage_Base.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
@@ skipping 14 matching lines @@
         return fCache->info();
     }
     SkAlphaType onAlphaType() const override {
         return fCache->info().alphaType();
     }
 
     bool onReadPixels(const SkImageInfo&, void*, size_t, int srcX, int srcY, CachingHint) const override;
     SkImageCacherator* peekCacherator() const override { return fCache; }
     SkData* onRefEncoded(GrContext*) const override;
     sk_sp<SkImage> onMakeSubset(const SkIRect&) const override;
+#if SK_SUPPORT_GPU
+    bool canGenerateTexture(const GrContextThreadSafeProxy& proxy) const override {
+        return fCache->canGenerateTexture(proxy);
+    }
+#endif
     bool getROPixels(SkBitmap*, CachingHint) const override;
     GrTexture* asTextureRef(GrContext*, const GrTextureParams&,
                             SkSourceGammaTreatment) const override;
     bool onIsLazyGenerated() const override { return true; }
 
 private:
     SkAutoTDelete<SkImageCacherator> fCache;
 
     typedef SkImage_Base INHERITED;
 };
@@ skipping 55 matching lines @@
 sk_sp<SkImage> SkImage::MakeFromGenerator(SkImageGenerator* generator, const SkIRect* subset) {
     if (!generator) {
         return nullptr;
     }
     SkImageCacherator* cache = SkImageCacherator::NewFromGenerator(generator, subset);
     if (!cache) {
         return nullptr;
     }
     return sk_make_sp<SkImage_Generator>(cache);
 }