Add subsetting to SkScaledCodec

tools/SkBitmapRegionCanvas.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.
  */
 
 #include "SkBitmap.h"
 #include "SkBitmapRegionDecoderInterface.h"
 #include "SkCodec.h"
@@ skipping 16 matching lines @@
     /*
      * Three differences from the Android version:
      *     Returns a Skia bitmap instead of an Android bitmap.
      *     Android version attempts to reuse a recycled bitmap.
      *     Removed the options object and used parameters for color type and
      *     sample size.
      */
     SkBitmap* decodeRegion(int start_x, int start_y, int width, int height,
                            int sampleSize, SkColorType prefColorType) override;
 
+    bool conversionSupported(SkColorType colorType) override;
+
 private:
 
     SkAutoTDelete<SkCodec> fDecoder;
 
     typedef SkBitmapRegionDecoderInterface INHERITED;
 
 };