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 "SkData.h"
@@ skipping 12 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&,
                             SkDestinationSurfaceColorMode) const override;
     bool onIsLazyGenerated() const override { return true; }
 
 private:
     mutable SkImageCacherator fCache;
 
     typedef SkImage_Base INHERITED;
 };
@@ skipping 44 matching lines @@
     SkImageCacherator::Validator validator(fCache.fSharedGenerator, &generatorSubset);
     return validator ? sk_sp<SkImage>(new SkImage_Generator(&validator)) : nullptr;
 }
 
 sk_sp<SkImage> SkImage::MakeFromGenerator(SkImageGenerator* generator, const SkIRect* subset) {
     SkImageCacherator::Validator validator(SkImageCacherator::SharedGenerator::Make(generator),
                                            subset);
 
     return validator ? sk_make_sp<SkImage_Generator>(&validator) : nullptr;
 }