add runtime option to provide data->imagegenerator factory

src/ports/SkImageGenerator_skia.cpp

 /*
  * Copyright 2015 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkData.h"
 #include "SkImageDecoder.h"
 #include "SkImageGenerator.h"
@@ skipping 90 matching lines @@
     bool onGetYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3],
                          SkYUVColorSpace* colorSpace) override {
         SkMemoryStream stream(fData->data(), fData->size(), false);
         return fDecoder->decodeYUV8Planes(&stream, sizes, planes, rowBytes, colorSpace);
     }
 
 private:
     typedef SkImageGenerator INHERITED;
 };
 
-SkImageGenerator* SkImageGenerator::NewFromData(SkData* data) {
-    if (NULL == data) {
-        return NULL;
-    }
-
+SkImageGenerator* SkImageGenerator::NewFromEncodedImpl(SkData* data) {
     SkMemoryStream stream(data->data(), data->size(), false);
     SkImageDecoder* decoder = SkImageDecoder::Factory(&stream);
     if (NULL == decoder) {
         return NULL;
     }
 
     SkBitmap bm;
     stream.rewind();
     if (!decoder->decode(&stream, &bm, kUnknown_SkColorType, SkImageDecoder::kDecodeBounds_Mode)) {
         SkDELETE(decoder);
         return NULL;
     }
 
     return SkNEW_ARGS(SkImageDecoderGenerator, (bm.info(), decoder, data));
 }