[webcrypto] Allow both ArrayBuffer and ArrayBufferView as inputs to crypto.subtle methods.

Source/wtf/ArrayPiece.h

Index: Source/wtf/ArrayPiece.h
diff --git a/Source/wtf/ArrayPiece.h b/Source/wtf/ArrayPiece.h
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+++ b/Source/wtf/ArrayPiece.h
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+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ArrayPiece_h
+#define ArrayPiece_h
+
+#include "wtf/Forward.h"
+#include "wtf/WTFExport.h"
+
+namespace WTF {
+
+// This class is for passing around un-owned bytes as a pointer + length.
+// It supports implicit conversion from several other data types.
+//
+// ArrayPiece has the concept of being "null". This is different from an empty
+// byte range. It is invalid to call methods other than isNull() on such
+// instances.
+//
+// IMPORTANT: The data contained by ArrayPiece is NOT OWNED, so caution must be
+//            taken to ensure it is kept alive.
+class WTF_EXPORT ArrayPiece {
+public:
+    // Constructs a "null" ArrayPiece object.
+    ArrayPiece();
+
+    ArrayPiece(void* data, unsigned byteLength);
+
+    // Constructs an ArrayPiece from the given ArrayBuffer. If the input is a
+    // nullptr, then the constructed instance will be isNull().
+    ArrayPiece(ArrayBuffer*);
+    ArrayPiece(ArrayBufferView*);
+
+    bool isNull() const;
+    void* data() const;
+    unsigned char* bytes() const;
+    unsigned byteLength() const;
+
+private:
+    void initWithData(void* data, unsigned byteLength);
+    void initNull();
+
+    void* m_data;
+    unsigned m_byteLength;
+    bool m_isNull;
+};
+
+} // namespace WTF
+
+using WTF::ArrayPiece;
+
+#endif // ArrayPiece_h