Add SkPngChunkReader.

src/ports/SkImageDecoder_empty.cpp

Index: src/ports/SkImageDecoder_empty.cpp
diff --git a/src/ports/SkImageDecoder_empty.cpp b/src/ports/SkImageDecoder_empty.cpp
index 624457b3bc92bbd5d276153281e3f8bae8b4b8ab..11c3db1afc519bb0639abd62c08cb7dae93552f1 100644
--- a/src/ports/SkImageDecoder_empty.cpp
+++ b/src/ports/SkImageDecoder_empty.cpp
@@ -14,6 +14,7 @@
 #include "SkStream.h"
 
 class SkColorTable;
+class SkPngChunkReader;
 
 // Empty implementations for SkImageDecoder.
 
@@ -60,7 +61,7 @@ const char* SkImageDecoder::GetFormatName(Format) {
     return nullptr;
 }
 
-SkImageDecoder::Peeker* SkImageDecoder::setPeeker(Peeker*) {
+SkPngChunkReader* SkImageDecoder::setPeeker(SkPngChunkReader*) {
     return nullptr;
 }