Fix version manager that flip flag in-flight does not make supported versions change.

net/quic/core/quic_protocol.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_QUIC_QUIC_PROTOCOL_H_
 #define NET_QUIC_QUIC_PROTOCOL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 598 matching lines @@
   // Called when an unrecoverable error is encountered.
   virtual void OnUnrecoverableError(QuicErrorCode error,
                                     const std::string& error_details,
                                     ConnectionCloseSource source) = 0;
 };
 
 // Used to generate filtered supported versions based on flags.
 class NET_EXPORT_PRIVATE QuicVersionManager {
  public:
   explicit QuicVersionManager(QuicVersionVector supported_versions);
-  ~QuicVersionManager();
+  virtual ~QuicVersionManager();
 
-  // Returns supported versions based on flags.
+  // Returns currently supported QUIC versions.
   const QuicVersionVector& GetSupportedVersions();
 
+ protected:
+  // Maybe refilter filtered_supported_versions_ based on flags.
+  void MaybeRefilterSupportedVersions();
+
+  // Refilters filtered_supported_versions_.
+  virtual void RefilterSupportedVersions();
+
+  const QuicVersionVector& filtered_supported_versions() const {
+    return filtered_supported_versions_;
+  }
+
  private:
   // FLAGS_quic_enable_version_36_v3
   bool enable_version_36_;
   // The list of versions that may be supported.
   QuicVersionVector allowed_supported_versions_;
   // This vector contains QUIC versions which are currently supported based
   // on flags.
   QuicVersionVector filtered_supported_versions_;
 };
 
@@ skipping 108 matching lines @@
   QuicPathId path_id;
   bool has_crypto_handshake;
   int num_padding_bytes;
   EncryptionLevel encryption_level;
   QuicPacketNumberLength packet_number_length;
 };
 
 }  // namespace net
 
 #endif  // NET_QUIC_QUIC_PROTOCOL_H_