Make the VER tag required in QUIC CHLO and SHLO messages.

net/quic/crypto/quic_crypto_server_config.cc

Index: net/quic/crypto/quic_crypto_server_config.cc
diff --git a/net/quic/crypto/quic_crypto_server_config.cc b/net/quic/crypto/quic_crypto_server_config.cc
index 52ff70908942f92f46c0045c89b854d75c33f4c1..26648a801f2ac701e36d2d5d5cccf4c2464be00d 100644
--- a/net/quic/crypto/quic_crypto_server_config.cc
+++ b/net/quic/crypto/quic_crypto_server_config.cc
@@ -484,18 +484,19 @@ QuicErrorCode QuicCryptoServerConfig::ProcessClientHello(
   // case, we need to make sure that we actually do not support this version
   // and that it wasn't a downgrade attack.
   QuicTag client_version_tag;
-  // TODO(rch): Make this check mandatory when we remove QUIC_VERSION_12.
-  if (client_hello.GetUint32(kVER, &client_version_tag) == QUIC_NO_ERROR) {
-    QuicVersion client_version = QuicTagToQuicVersion(client_version_tag);
-    if (client_version != version) {
-      // Just because client_version is a valid version enum doesn't mean that
-      // this server actually supports that version, so we check to see if
-      // it's actually in the supported versions list.
-      for (size_t i = 0; i < supported_versions.size(); ++i) {
-        if (client_version == supported_versions[i]) {
-          *error_details = "Downgrade attack detected";
-          return QUIC_VERSION_NEGOTIATION_MISMATCH;
-        }
+  if (client_hello.GetUint32(kVER, &client_version_tag) != QUIC_NO_ERROR) {
+    *error_details = "client hello missing version list";
+    return QUIC_INVALID_CRYPTO_MESSAGE_PARAMETER;
+  }
+  QuicVersion client_version = QuicTagToQuicVersion(client_version_tag);
+  if (client_version != version) {
+    // Just because client_version is a valid version enum doesn't mean that
+    // this server actually supports that version, so we check to see if
+    // it's actually in the supported versions list.
+    for (size_t i = 0; i < supported_versions.size(); ++i) {
+      if (client_version == supported_versions[i]) {
+        *error_details = "Downgrade attack detected";
+        return QUIC_VERSION_NEGOTIATION_MISMATCH;
       }
     }
   }