Replace QuicString with std::string, pass 1

This replaces QuicString with std::string in all of the "QUIC proper".  I will
delete QuicString once all code using it is gone.

gfe-relnote: n/a (no functional change)
PiperOrigin-RevId: 237872023
Change-Id: I82de62c9855516b15039734d05155917e68ff4ee
diff --git a/quic/core/chlo_extractor_test.cc b/quic/core/chlo_extractor_test.cc
index 1e0b6f5..cb5fd59 100644
--- a/quic/core/chlo_extractor_test.cc
+++ b/quic/core/chlo_extractor_test.cc
@@ -35,12 +35,12 @@
 
   QuicConnectionId connection_id() const { return connection_id_; }
   QuicTransportVersion transport_version() const { return version_; }
-  const QuicString& chlo() const { return chlo_; }
+  const std::string& chlo() const { return chlo_; }
 
  private:
   QuicConnectionId connection_id_;
   QuicTransportVersion version_;
-  QuicString chlo_;
+  std::string chlo_;
 };
 
 class ChloExtractorTest : public QuicTest {
@@ -105,7 +105,7 @@
   CryptoHandshakeMessage client_hello;
   client_hello.set_tag(kCHLO);
 
-  QuicString client_hello_str(client_hello.GetSerialized().AsStringPiece());
+  std::string client_hello_str(client_hello.GetSerialized().AsStringPiece());
   // Construct a CHLO with each supported version
   for (ParsedQuicVersion version : AllSupportedVersions()) {
     SCOPED_TRACE(version);
@@ -135,7 +135,7 @@
   CryptoHandshakeMessage client_hello;
   client_hello.set_tag(kCHLO);
 
-  QuicString client_hello_str(client_hello.GetSerialized().AsStringPiece());
+  std::string client_hello_str(client_hello.GetSerialized().AsStringPiece());
   MakePacket(AllSupportedVersions()[0], client_hello_str,
              /*munge_offset*/ false, /*munge_stream_id*/ true);
   EXPECT_FALSE(ChloExtractor::Extract(*packet_, AllSupportedVersions(), {},
@@ -147,7 +147,7 @@
   CryptoHandshakeMessage client_hello;
   client_hello.set_tag(kCHLO);
 
-  QuicString client_hello_str(client_hello.GetSerialized().AsStringPiece());
+  std::string client_hello_str(client_hello.GetSerialized().AsStringPiece());
   MakePacket(AllSupportedVersions()[0], client_hello_str, /*munge_offset*/ true,
              /*munge_stream_id*/ false);
   EXPECT_FALSE(ChloExtractor::Extract(*packet_, AllSupportedVersions(), {},