Adds CryptoHandshakeMessage::HasStringPiece method.

net/quic/core/crypto/crypto_handshake_message.h

Index: net/quic/core/crypto/crypto_handshake_message.h
diff --git a/net/quic/core/crypto/crypto_handshake_message.h b/net/quic/core/crypto/crypto_handshake_message.h
index ab4f238a071a89cb7805c97b503e96476c670651..e4dccc3b5a8430d013d0dd5e6d7d85db2c80ed31 100644
--- a/net/quic/core/crypto/crypto_handshake_message.h
+++ b/net/quic/core/crypto/crypto_handshake_message.h
@@ -83,6 +83,7 @@ class NET_EXPORT_PRIVATE CryptoHandshakeMessage {
                            size_t* out_len) const;
 
   bool GetStringPiece(QuicTag tag, base::StringPiece* out) const;
+  bool HasStringPiece(QuicTag tag) const;
 
   // GetNthValue24 interprets the value with the given tag to be a series of
   // 24-bit, length prefixed values and it returns the subvalue with the given