Implement basic classes for HPACK (HTTP/2 compression)

net/spdy/hpack_string_util.h

+#ifndef NET_SPDY_HPACK_STRING_UTIL_H_
+#define NET_SPDY_HPACK_STRING_UTIL_H_
+
+#include "base/strings/string_piece.h"
+
+namespace net {
+
+// All section references below are to
+// http://tools.ietf.org/html/draft-ietf-httpbis-header-compression-04
+// .
+
+// A constant-time StringPiece comparison function, as suggested
+// by section 6.
+bool StringPiecesEqualConstantTime(base::StringPiece str1,
+                                   base::StringPiece str2);
+
+}  // namespace net
+
+#endif  // NET_SPDY_HPACK_STRING_UTIL_H_