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

net/quic/core/quic_protocol.h

Index: net/quic/core/quic_protocol.h
diff --git a/net/quic/core/quic_protocol.h b/net/quic/core/quic_protocol.h
index 1c3e3add689e9cd7bbf96e00b3100c39a8b78f0f..fc5042d9db5dde7ba4dfc1eb5f2fed6a40960ddb 100644
--- a/net/quic/core/quic_protocol.h
+++ b/net/quic/core/quic_protocol.h
@@ -616,11 +616,22 @@ class NET_EXPORT_PRIVATE QuicConnectionCloseDelegateInterface {
 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_;