Make BitmapRegionDecoder succeed on invalid requests

src/android/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 "SkBitmapRegionDecoder.h"
 #include "SkCodec.h"
 
 /*
  * This class implements SkBitmapRegionDecoder using an SkCodec and
  * an SkCanvas.  It uses the scanline decoder to subset the height.  It then
  * will subset the width and scale by drawing to an SkCanvas.
  */
-// FIXME (msarett): This implementation does not support WEBP, because WEBP
-// does not have a scanline decoder.
+// FIXME: This class works well as a performance/quality comparison for
+//        SkBitmapRegionCodec, but it lacks several capabilities that are
+//        required by BitmapRegionDecoder in Android.
+//        (1) WEBP decodes - because SkWebpCodec does not have a scanline
+//            decoder.
+//        (2) Decodes to kGray8 and kIndex8.
+//        (3) Decodes to kUnpremul.
+//        (4) Correcting an invalid dstColorType.  For example, if the
+//            client requests kRGB_565 for a non-opaque image, rather than
+//            fail, we need to go ahead and decode to kN32.
 class SkBitmapRegionCanvas : public SkBitmapRegionDecoder {
 public:
 
     /*
      * Takes ownership of pointer to decoder
      */
     SkBitmapRegionCanvas(SkCodec* decoder);
 
     bool decodeRegion(SkBitmap* bitmap, SkBRDAllocator* allocator,
                       const SkIRect& desiredSubset, int sampleSize,
                       SkColorType colorType, bool requireUnpremul) override;
 
     bool conversionSupported(SkColorType colorType) override;
 
     SkEncodedFormat getEncodedFormat() override { return fDecoder->getEncodedFormat(); }
 
 private:
 
     SkAutoTDelete<SkCodec> fDecoder;
 
     typedef SkBitmapRegionDecoder INHERITED;
 
 };