Use std::string instead of string in a few places in QUIC to permit chrome merge.

gfe-relnote: n/a - just adding std:: prefix.
PiperOrigin-RevId: 239062252
Change-Id: I7351ad10d7445eb2c9dd1fc7a6bb5e91c09273a9

quic/core/crypto/crypto_utils.cc

diff --git a/quic/core/crypto/crypto_utils.cc b/quic/core/crypto/crypto_utils.cc
index e3e438b..7580bbb 100644
--- a/quic/core/crypto/crypto_utils.cc
+++ b/quic/core/crypto/crypto_utils.cc
@@ -458,7 +458,7 @@
 std::string CryptoUtils::HashHandshakeMessage(
     const CryptoHandshakeMessage& message,
     Perspective perspective) {
-  string output;
+  std::string output;
   const QuicData& serialized = message.GetSerialized();
   uint8_t digest[SHA256_DIGEST_LENGTH];
   SHA256(reinterpret_cast<const uint8_t*>(serialized.data()),

quic/core/crypto/crypto_utils.h

diff --git a/quic/core/crypto/crypto_utils.h b/quic/core/crypto/crypto_utils.h
index a958311..b881778 100644
--- a/quic/core/crypto/crypto_utils.h
+++ b/quic/core/crypto/crypto_utils.h
@@ -198,8 +198,8 @@
       HandshakeFailureReason reason);
 
   // Returns a hash of the serialized |message|.
-  static string HashHandshakeMessage(const CryptoHandshakeMessage& message,
-                                     Perspective perspective);
+  static std::string HashHandshakeMessage(const CryptoHandshakeMessage& message,
+                                          Perspective perspective);
 
  private:
   // Implements the HKDF-Expand-Label function as defined in section 7.1 of RFC

quic/core/quic_connection.cc

diff --git a/quic/core/quic_connection.cc b/quic/core/quic_connection.cc
index ffc4093..3ead1d2 100644
--- a/quic/core/quic_connection.cc
+++ b/quic/core/quic_connection.cc
@@ -1998,7 +1998,7 @@
     // Configured to accept any packet number in range 1...0x7fffffff as initial
     // packet number.
     bool out_of_bound = false;
-    string error_detail = "Packet number out of bounds.";
+    std::string error_detail = "Packet number out of bounds.";
     if (last_header_.packet_number.IsInitialized()) {
       out_of_bound = !Near(packet_number, last_header_.packet_number);
     } else if ((packet_number > MaxRandomInitialPacketNumber())) {