Make SkCodec support peek() and read()

src/codec/SkBmpCodec.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.
  */
 #ifndef SkBmpCodec_DEFINED
 #define SkBmpCodec_DEFINED
 
 #include "SkCodec.h"
 #include "SkColorTable.h"
 #include "SkImageInfo.h"
 #include "SkStream.h"
 #include "SkSwizzler.h"
 #include "SkTypes.h"
 
 /*
  * This class enables code sharing between its bmp codec subclasses.  The
  * subclasses actually do the work.
  */
 class SkBmpCodec : public SkCodec {
 public:
-
-    /*
-     * Checks the start of the stream to see if the image is a bmp
-     */
-    static bool IsBmp(SkStream*);
+    static bool IsBmp(const void*, size_t);
 
     /*
      * Assumes IsBmp was called and returned true
      * Creates a bmp decoder
      * Reads enough of the stream to determine the image format
      */
     static SkCodec* NewFromStream(SkStream*);
 
     /*
      * Creates a bmp decoder for a bmp embedded in ico
@@ skipping 100 matching lines @@
 
     // TODO(msarett): Override default skipping with something more clever.
 
     const uint16_t          fBitsPerPixel;
     const SkScanlineOrder   fRowOrder;
 
     typedef SkCodec INHERITED;
 };
 
 #endif