Add SkPngChunkReader.

src/codec/SkCodec.cpp

Index: src/codec/SkCodec.cpp
diff --git a/src/codec/SkCodec.cpp b/src/codec/SkCodec.cpp
index a49586ffeb1ecf6ff337b1dc12fd0fe8120be113..ea318fbb86aa0bca9f8c41da5eefdcbe3ae01381 100644
--- a/src/codec/SkCodec.cpp
+++ b/src/codec/SkCodec.cpp
@@ -18,15 +18,25 @@ struct DecoderProc {
 };
 
 static const DecoderProc gDecoderProcs[] = {
-    { SkPngCodec::IsPng, SkPngCodec::NewFromStream },
     { SkIcoCodec::IsIco, SkIcoCodec::NewFromStream },
     { SkBmpCodec::IsBmp, SkBmpCodec::NewFromStream }
 };
 
-SkCodec* SkCodec::NewFromStream(SkStream* stream) {
+SkCodec* SkCodec::NewFromStream(SkStream* stream, SkChunkReader* chunkReader) {
     if (!stream) {
         return NULL;
     }
+
+    // PNG is special, since we want to be able to supply an SkChunkReader.
+    // But this code follows the same pattern as the loop.
+    const bool isPng = SkPngCodec::IsPng(stream);
+    if (!stream->rewind()) {
+        return NULL;
+    }
+    if (isPng) {
+        return SkPngCodec::NewFromStream(stream, chunkReader);
+    }
+
     for (uint32_t i = 0; i < SK_ARRAY_COUNT(gDecoderProcs); i++) {
         DecoderProc proc = gDecoderProcs[i];
         const bool correctFormat = proc.IsFormat(stream);
@@ -40,11 +50,11 @@ SkCodec* SkCodec::NewFromStream(SkStream* stream) {
     return NULL;
 }
 
-SkCodec* SkCodec::NewFromData(SkData* data) {
+SkCodec* SkCodec::NewFromData(SkData* data, SkChunkReader* reader) {
     if (!data) {
         return NULL;
     }
-    return NewFromStream(SkNEW_ARGS(SkMemoryStream, (data)));
+    return NewFromStream(SkNEW_ARGS(SkMemoryStream, (data)), reader);
 }
 
 SkCodec::SkCodec(const SkImageInfo& info, SkStream* stream)