Make SkCodec support peek() and read()

src/codec/SkCodec_libico.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 "SkBmpCodec.h"
 #include "SkCodec_libico.h"
 #include "SkCodec_libpng.h"
@@ skipping 37 matching lines @@
         default:
             SkASSERT(false);
             break;
     }
     return dstInfo.makeAlphaType(embeddedAlpha);
 }
 
 /*
  * Checks the start of the stream to see if the image is an Ico or Cur
  */
-bool SkIcoCodec::IsIco(SkStream* stream) {
+bool SkIcoCodec::IsIco(const void* buffer, size_t bytesRead) {
     const char icoSig[] = { '\x00', '\x00', '\x01', '\x00' };
     const char curSig[] = { '\x00', '\x00', '\x02', '\x00' };
-    char buffer[sizeof(icoSig)];
-    return stream->read(buffer, sizeof(icoSig)) == sizeof(icoSig) &&
+    return bytesRead >= sizeof(icoSig) &&
             (!memcmp(buffer, icoSig, sizeof(icoSig)) ||
             !memcmp(buffer, curSig, sizeof(curSig)));
 }
 
 /*
  * Assumes IsIco was called and returned true
  * Creates an Ico decoder
  * Reads enough of the stream to determine the image format
  */
 SkCodec* SkIcoCodec::NewFromStream(SkStream* stream) {
@@ skipping 96 matching lines @@
         SkAutoTUnref<SkData> data(
                 SkData::NewFromStream(inputStream.get(), size));
         if (nullptr == data.get()) {
             SkCodecPrintf("Warning: could not create embedded stream.\n");
             break;
         }
         SkAutoTDelete<SkMemoryStream> embeddedStream(new SkMemoryStream(data.get()));
         bytesRead += size;
 
         // Check if the embedded codec is bmp or png and create the codec
-        const bool isPng = SkPngCodec::IsPng(embeddedStream);
-        SkAssertResult(embeddedStream->rewind());
         SkCodec* codec = nullptr;
-        if (isPng) {
+        if (SkPngCodec::IsPng((const char*) data->bytes(), data->size())) {
             codec = SkPngCodec::NewFromStream(embeddedStream.detach());
         } else {
             codec = SkBmpCodec::NewFromIco(embeddedStream.detach());
         }
 
         // Save a valid codec
         if (nullptr != codec) {
             codecs->push_back().reset(codec);
         }
     }
@@ skipping 179 matching lines @@
 SkCodec::SkScanlineOrder SkIcoCodec::onGetScanlineOrder() const {
     // FIXME: This function will possibly return the wrong value if it is called
     //        before startScanlineDecode().
     return fCurrScanlineCodec ? fCurrScanlineCodec->getScanlineOrder() :
             INHERITED::onGetScanlineOrder();
 }
 
 SkSampler* SkIcoCodec::getSampler(bool createIfNecessary) {
     return fCurrScanlineCodec ? fCurrScanlineCodec->getSampler(createIfNecessary) : nullptr;
 }