Store client cert hashes as strings instead of StringPieces.

net/quic/crypto/crypto_handshake.h

Index: net/quic/crypto/crypto_handshake.h
diff --git a/net/quic/crypto/crypto_handshake.h b/net/quic/crypto/crypto_handshake.h
index b97bd68f6ef00150bea1ee746b8c4f66f76d477a..bfd2f347fd854d7a636241ad23556fbddce63b8a 100644
--- a/net/quic/crypto/crypto_handshake.h
+++ b/net/quic/crypto/crypto_handshake.h
@@ -9,7 +9,6 @@
 #include <vector>
 
 #include "base/memory/scoped_ptr.h"
-#include "base/strings/string_piece.h"
 #include "net/base/net_export.h"
 #include "net/quic/quic_protocol.h"
 
@@ -130,8 +129,8 @@ struct NET_EXPORT_PRIVATE QuicCryptoNegotiatedParameters {
   bool x509_ecdsa_supported;
 
   // Used to generate cert chain when sending server config updates.
-  base::StringPiece client_common_set_hashes;
-  base::StringPiece client_cached_cert_hashes;
+  std::string client_common_set_hashes;
+  std::string client_cached_cert_hashes;
 };
 
 // QuicCryptoConfig contains common configuration between clients and servers.