Remove some duplicate code in quic tests.

net/quic/test_tools/quic_test_utils.h

Index: net/quic/test_tools/quic_test_utils.h
diff --git a/net/quic/test_tools/quic_test_utils.h b/net/quic/test_tools/quic_test_utils.h
index 86c5caaf72bf47e2909189a6495d9de698cc071b..ce0776ef81ca1ee166551e41cfc1659d58044d23 100644
--- a/net/quic/test_tools/quic_test_utils.h
+++ b/net/quic/test_tools/quic_test_utils.h
@@ -37,6 +37,8 @@ void CompareCharArraysWithHexError(const std::string& description,
                                    const char* expected,
                                    const int expected_len);
 
+bool DecodeHexString(const base::StringPiece& hex, std::string* bytes);
+
 // Returns the length of a QuicPacket that is capable of holding either a
 // stream frame or a minimal ack frame.  Sets |*payload_length| to the number
 // of bytes of stream data that will fit in such a packet.