Make SkCodec support peek() and read()

src/codec/SkCodec_wbmp.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 SkCodec_wbmp_DEFINED
 #define SkCodec_wbmp_DEFINED
 
 #include "SkCodec.h"
 #include "SkSwizzler.h"
 
 class SkWbmpCodec final : public SkCodec {
 public:
-    static bool IsWbmp(SkStream*);
+    static bool IsWbmp(const void*, size_t);
 
     /*
      * Assumes IsWbmp was called and returned true
      * Creates a wbmp codec
      * Takes ownership of the stream
      */
     static SkCodec* NewFromStream(SkStream*);
 
 protected:
     SkEncodedFormat onGetEncodedFormat() const override;
@@ skipping 27 matching lines @@
 
     // FIXME: Override onSkipScanlines to avoid swizzling.
     int onGetScanlines(void* dst, int count, size_t dstRowBytes) override;
     Result onStartScanlineDecode(const SkImageInfo& dstInfo, const Options& options,
             SkPMColor inputColorTable[], int* inputColorCount) override;
 
     typedef SkCodec INHERITED;
 };
 
 #endif  // SkCodec_wbmp_DEFINED