Allow SkAndroidCodec to use SkPngChunkReader

include/codec/SkAndroidCodec.h

Index: include/codec/SkAndroidCodec.h
diff --git a/include/codec/SkAndroidCodec.h b/include/codec/SkAndroidCodec.h
index e33116f9ba0c52f1fc665b34bcaf88a586c86ce0..5f1c16418dcc73a3e00a4f167a8462b202555162 100644
--- a/include/codec/SkAndroidCodec.h
+++ b/include/codec/SkAndroidCodec.h
@@ -23,18 +23,24 @@ public:
      *  If this stream represents an encoded image that we know how to decode,
      *  return an SkAndroidCodec that can decode it. Otherwise return NULL.
      *
+     *  If SkPngChunkReader is not NULL, take a ref and pass it to libpng if
+     *  the image is a png.

[djsollen, 2015/11/30 15:42:22]

what is the expected behavior if you pass in a chunkReader if the image is not a
PNG or it is a PNG but not a 9patch?  I assume it succeeds but doesn't modify
the chunkReader

[msarett, 2015/11/30 15:44:33]

Me too.  Leon, can you confirm?

[scroggo, 2015/11/30 15:55:09]

If the image is not a PNG, no ref is taken.

If it *is* a PNG, we don't actually know whether the image is a ninepatch - it's
the SkPngChunkReader's job to determine that. So it gets reffed, and if the PNG
has unknown chunks, SkPngChunkReader's callback will get called.

These comments match the comments in SkCodec. If we update these, we should
update SkCodec as well.
The only way chunkReader can affect whether NewFrom*** succeeds is if its
implementation of readChunk returns false.

And chunkReader is never modified (besides changing its refcount), unless
readChunk modifies it.

[djsollen, 2015/11/30 15:58:47]

Can you update the comment in SkCodec?  I'm fine if this comment is more spartan
and points the reader to the larger description in SkCodec.

+     *
      *  If NULL is returned, the stream is deleted immediately. Otherwise, the
      *  SkCodec takes ownership of it, and will delete it when done with it.
      */
-    static SkAndroidCodec* NewFromStream(SkStream*);
+    static SkAndroidCodec* NewFromStream(SkStream*, SkPngChunkReader* = NULL);
 
     /**
      *  If this data represents an encoded image that we know how to decode,
      *  return an SkAndroidCodec that can decode it. Otherwise return NULL.
      *
+     *  If SkPngChunkReader is not NULL, take a ref and pass it to libpng if
+     *  the image is a png.
+     *
      *  Will take a ref if it returns a codec, else will not affect the data.
      */
-    static SkAndroidCodec* NewFromData(SkData*);
+    static SkAndroidCodec* NewFromData(SkData*, SkPngChunkReader* = NULL);
 
     virtual ~SkAndroidCodec() {}