Add SkPngChunkReader.

src/codec/SkCodec_libpng.cpp

Index: src/codec/SkCodec_libpng.cpp
diff --git a/src/codec/SkCodec_libpng.cpp b/src/codec/SkCodec_libpng.cpp
index 4850235c0794ab591e8e16167d0409be214a313c..bc4f35f017c863ee566842bbd953300f86f24728 100644
--- a/src/codec/SkCodec_libpng.cpp
+++ b/src/codec/SkCodec_libpng.cpp
@@ -66,6 +66,14 @@ static void sk_read_fn(png_structp png_ptr, png_bytep data,
     }
 }
 
+#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
+static int sk_read_user_chunk(png_structp png_ptr, png_unknown_chunkp chunk) {
+    SkChunkReader* chunkReader = (SkChunkReader*)png_get_user_chunk_ptr(png_ptr);
+    // peek() returning true means continue decoding
+    return chunkReader->readChunk((const char*)chunk->name, chunk->data, chunk->size) ? 1 : -1;
+}
+#endif
+
 ///////////////////////////////////////////////////////////////////////////////
 // Helpers
 ///////////////////////////////////////////////////////////////////////////////
@@ -201,7 +209,7 @@ bool SkPngCodec::IsPng(SkStream* stream) {
     return true;
 }
 
-SkCodec* SkPngCodec::NewFromStream(SkStream* stream) {
+SkCodec* SkPngCodec::NewFromStream(SkStream* stream, SkChunkReader* chunkReader) {
     // The image is known to be a PNG. Decode enough to know the SkImageInfo.
     png_structp png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL,
                                                  sk_error_fn, sk_warning_fn);
@@ -226,10 +234,13 @@ SkCodec* SkPngCodec::NewFromStream(SkStream* stream) {
 
     png_set_read_fn(png_ptr, static_cast<void*>(stream), sk_read_fn);
 
-    // FIXME: This is where the old code hooks up the Peeker. Does it need to
-    // be set this early? (i.e. where are the user chunks? early in the stream,
-    // potentially?)
-    // If it does, we need to figure out a way to set it here.
+#ifdef PNG_READ_UNKNOWN_CHUNKS_SUPPORTED
+    // hookup our chunkReader so we can see any user-chunks the caller may be interested in
+    if (chunkReader) {
+        png_set_keep_unknown_chunks(png_ptr, PNG_HANDLE_CHUNK_ALWAYS, (png_byte*)"", 0);
+        png_set_read_user_chunk_fn(png_ptr, (png_voidp) chunkReader, sk_read_user_chunk);
+    }
+#endif
 
     // The call to png_read_info() gives us all of the information from the
     // PNG file before the first IDAT (image data chunk).
@@ -327,15 +338,16 @@ SkCodec* SkPngCodec::NewFromStream(SkStream* stream) {
 
     SkImageInfo info = SkImageInfo::Make(origWidth, origHeight, skColorType,
                                          skAlphaType);
-    SkCodec* codec = SkNEW_ARGS(SkPngCodec, (info, stream, png_ptr, info_ptr));
+    SkCodec* codec = SkNEW_ARGS(SkPngCodec, (info, stream, chunkReader, png_ptr, info_ptr));
     autoClean.detach();
     return codec;
 }
 
 #define INVALID_NUMBER_PASSES -1
-SkPngCodec::SkPngCodec(const SkImageInfo& info, SkStream* stream,
+SkPngCodec::SkPngCodec(const SkImageInfo& info, SkStream* stream, SkChunkReader* chunkReader,
                        png_structp png_ptr, png_infop info_ptr)
     : INHERITED(info, stream)
+    , fChunkReader(SkSafeRef(chunkReader))
     , fPng_ptr(png_ptr)
     , fInfo_ptr(info_ptr)
     , fSrcConfig(SkSwizzler::kUnknown)