Revert of Add SkPngChunkReader.

src/images/SkImageDecoder.cpp

Index: src/images/SkImageDecoder.cpp
diff --git a/src/images/SkImageDecoder.cpp b/src/images/SkImageDecoder.cpp
index 221faf74d5e33cf0160e765c3887c69a7e7b3a45..d2ad553769b3100427b79325b54910d6786b79e3 100644
--- a/src/images/SkImageDecoder.cpp
+++ b/src/images/SkImageDecoder.cpp
@@ -83,7 +83,7 @@
     return "Unknown Format";
 }
 
-SkPngChunkReader* SkImageDecoder::setPeeker(SkPngChunkReader* peeker) {
+SkImageDecoder::Peeker* SkImageDecoder::setPeeker(Peeker* peeker) {
     SkRefCnt_SafeAssign(fPeeker, peeker);
     return peeker;
 }