Add SkPngChunkReader.

src/codec/SkCodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCodec.h"
 #include "SkData.h"
 #include "SkCodec_libbmp.h"
 #include "SkCodec_libico.h"
 #include "SkCodec_libpng.h"
 #include "SkStream.h"
 
 struct DecoderProc {
     bool (*IsFormat)(SkStream*);
     SkCodec* (*NewFromStream)(SkStream*);
 };
 
 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);
         if (!stream->rewind()) {
             return NULL;
         }
         if (correctFormat) {
             return proc.NewFromStream(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)
     : INHERITED(info)
 #ifdef SK_SUPPORT_LEGACY_BOOL_ONGETINFO
     , fInfo(info)
 #endif
     , fStream(stream)
     , fNeedsRewind(false)
 {}
 
 bool SkCodec::rewindIfNeeded() {
     // Store the value of fNeedsRewind so we can update it. Next read will
     // require a rewind.
     const bool neededRewind = fNeedsRewind;
     fNeedsRewind = true;
     return !neededRewind || fStream->rewind();
 }
 
 SkScanlineDecoder* SkCodec::getScanlineDecoder(const SkImageInfo& dstInfo) {
     fScanlineDecoder.reset(NULL);
     if (!rewindIfNeeded()) {
         return NULL;
     }
     fScanlineDecoder.reset(this->onGetScanlineDecoder(dstInfo));
     return fScanlineDecoder.get();
 }