Make SkCodec support peek() and read()

src/codec/SkCodec_libico.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"
 #include "SkTypes.h"
 
 /*
  * This class implements the decoding for bmp images
  */
 class SkIcoCodec : public SkCodec {
 public:
-
-    /*
-     * Checks the start of the stream to see if the image is a Ico or Cur
-     */
-    static bool IsIco(SkStream*);
+    static bool IsIco(const void*, size_t);
 
     /*
      * Assumes IsIco was called and returned true
      * Creates an Ico decoder
      * Reads enough of the stream to determine the image format
      */
     static SkCodec* NewFromStream(SkStream*);
 
 protected:
 
@@ skipping 49 matching lines @@
     // 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;
 
     typedef SkCodec INHERITED;
 };