Refactor SkBitmapRegionDecoderInterface for Android

tools/SkBitmapRegionSampler.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 "SkImageDecoder.h"
 #include "SkTemplates.h"
 
 /*
  * This class aims to duplicate the current implementation of
  * SkBitmapRegionDecoder in Android.
  */
 class SkBitmapRegionSampler : public SkBitmapRegionDecoderInterface {
 public:
 
     /*
      * Takes ownership of pointer to decoder
      */
     SkBitmapRegionSampler(SkImageDecoder* decoder, int width, int height);
 
-    /*
-     * 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 prepareRegion(const SkIRect& desiredSubset, int sampleSize,
+            SkColorType colorType, bool requireUnpremul, SkImageInfo* outSize) override;
 
-    bool conversionSupported(SkColorType colorType) override {
-        // SkBitmapRegionSampler does not allow the client to check if the conversion
-        // is supported.  We will return true as a default.  If the conversion is in
-        // fact not supported, decodeRegion() will ignore the prefColorType and choose
-        // its own color type.  We catch this and fail non-fatally in our test code.
-        return true;
-    }
+    bool decodeRegion(SkBitmap& bitmap) override;
 
 private:
 
     SkAutoTDelete<SkImageDecoder> fDecoder;
 
+
+    // Fields set by prepareRegion()
+    SkIRect     fSubset;     // Subset of the original image to decode
+    SkColorType fColorType;  // Color type to decode to
+
     typedef SkBitmapRegionDecoderInterface INHERITED;
 
 };