Make SkPngCodec decode progressively.

src/codec/SkIcoCodec.h

 /*
  * 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 "SkImageInfo.h"
 #include "SkStream.h"
@@ skipping 36 matching lines @@
 
 private:
 
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const SkCodec::Options& options,
             SkPMColor inputColorPtr[], int* inputColorCount) override;
 
     int onGetScanlines(void* dst, int count, size_t rowBytes) override;
 
     bool onSkipScanlines(int count) override;
 
+    Result onStartIncrementalDecode(const SkImageInfo& dstInfo, void* pixels, size_t rowBytes,
+            const SkCodec::Options&, SkPMColor*, int*) override;
+
+    Result onIncrementalDecode(int* rowsDecoded) override;
+
     SkSampler* getSampler(bool createIfNecessary) override;
 
     /*
      * Searches fEmbeddedCodecs for a codec that matches requestedSize.
      * The search starts at startIndex and ends when an appropriate codec
      * is found, or we have reached the end of the array.
      *
      * @return the index of the matching codec or -1 if there is no
      *         matching codec between startIndex and the end of
      *         the array.
@@ skipping 10 matching lines @@
     SkAutoTDelete<SkTArray<SkAutoTDelete<SkCodec>, true>> fEmbeddedCodecs; // owned
 
     // Only used by the scanline decoder.  onStartScanlineDecode() will set
     // fCurrScanlineCodec to one of the fEmbeddedCodecs, if it can find a
     // codec of the appropriate size.  We will use fCurrScanlineCodec for
     // subsequent calls to onGetScanlines() or onSkipScanlines().
     // fCurrScanlineCodec is owned by this class, but should not be an
     // SkAutoTDelete.  It will be deleted by the destructor of fEmbeddedCodecs.
     SkCodec* fCurrScanlineCodec;
 
+    // Only used by incremental decoder.  onStartIncrementalDecode() will set
+    // fCurrIncrementalCodec to one of the fEmbeddedCodecs, if it can find a
+    // codec of the appropriate size.  We will use fCurrIncrementalCodec for
+    // subsequent calls to incrementalDecode().
+    // fCurrIncrementalCodec is owned by this class, but should not be an
+    // SkAutoTDelete.  It will be deleted by the destructor of fEmbeddedCodecs.
+    SkCodec* fCurrIncrementalCodec;
+
     typedef SkCodec INHERITED;
 };