Factor QuicCryptoClientStream APIs into QuicCryptoClientStreamBase.

net/quic/crypto/quic_crypto_client_config.cc

Index: net/quic/crypto/quic_crypto_client_config.cc
diff --git a/net/quic/crypto/quic_crypto_client_config.cc b/net/quic/crypto/quic_crypto_client_config.cc
index 8d46239e2e56db570e81e56dad7eba153ad97303..0c5c3c984e31553b9db6a0acf50da2cf180f9808 100644
--- a/net/quic/crypto/quic_crypto_client_config.cc
+++ b/net/quic/crypto/quic_crypto_client_config.cc
@@ -773,32 +773,11 @@ QuicErrorCode QuicCryptoClientConfig::ProcessServerHello(
     string* error_details) {
   DCHECK(error_details != nullptr);
 
-  if (server_hello.tag() != kSHLO) {
-    *error_details = "Bad tag";
-    return QUIC_INVALID_CRYPTO_MESSAGE_TYPE;
-  }
 
-  const QuicTag* supported_version_tags;
-  size_t num_supported_versions;
-
-  if (server_hello.GetTaglist(kVER, &supported_version_tags,
-                              &num_supported_versions) != QUIC_NO_ERROR) {
-    *error_details = "server hello missing version list";
-    return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
-  }
-  if (!negotiated_versions.empty()) {
-    bool mismatch = num_supported_versions != negotiated_versions.size();
-    for (size_t i = 0; i < num_supported_versions && !mismatch; ++i) {
-      mismatch = QuicTagToQuicVersion(supported_version_tags[i]) !=
-          negotiated_versions[i];
-    }
-    // The server sent a list of supported versions, and the connection
-    // reports that there was a version negotiation during the handshake.
-      // Ensure that these two lists are identical.
-    if (mismatch) {
-      *error_details = "Downgrade attack detected";
-      return QUIC_VERSION_NEGOTIATION_MISMATCH;
-    }
+  QuicErrorCode valid = CryptoUtils::ValidateServerHello(
+      server_hello, negotiated_versions, error_details);
+  if (valid != QUIC_NO_ERROR) {
+    return valid;
   }
 
   // Learn about updated source address tokens.