Add QuicStringPiece which is actually StringPiece.

net/quic/test_tools/failing_proof_source.h

 // 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.
 
 #ifndef NET_QUIC_TEST_TOOLS_FAILING_PROOF_SOURCE_H_
 #define NET_QUIC_TEST_TOOLS_FAILING_PROOF_SOURCE_H_
 
 #include "net/quic/core/crypto/proof_source.h"
+#include "net/quic/platform/api/quic_string_piece.h"
 
 namespace net {
 namespace test {
 
 class FailingProofSource : public ProofSource {
  public:
   void 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) override;
 };
 
 }  // namespace test
 }  // namespace net
 
 #endif  // NET_QUIC_TEST_TOOLS_FAILING_PROOF_SOURCE_H_