Add QuicStringPiece which is actually StringPiece.

net/quic/test_tools/failing_proof_source.cc

 // Copyright (c) 2017 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.
 
 #include "net/quic/test_tools/failing_proof_source.h"
 
 namespace net {
 namespace test {
 
 void FailingProofSource::GetProof(const QuicSocketAddress& server_address,
                                   const std::string& hostname,
                                   const std::string& server_config,
                                   QuicVersion quic_version,
-                                  base::StringPiece chlo_hash,
+                                  QuicStringPiece chlo_hash,
                                   const QuicTagVector& connection_options,
                                   std::unique_ptr<Callback> callback) {
   callback->Run(false, nullptr, QuicCryptoProof(), nullptr);
 }
 
 }  // namespace test
 }  // namespace net