Add QuicConnectionCloseDelegateInterface. No functional change expected. Not protected.

net/quic/quic_protocol.h

Index: net/quic/quic_protocol.h
diff --git a/net/quic/quic_protocol.h b/net/quic/quic_protocol.h
index 467187d36f74091102e02a668a2f54c77e1fdd97..147d1c1c6a6fdd9e7dba45656dfd3b7f0c0cb613 100644
--- a/net/quic/quic_protocol.h
+++ b/net/quic/quic_protocol.h
@@ -1352,6 +1352,17 @@ class NET_EXPORT_PRIVATE QuicAckListenerInterface
   virtual ~QuicAckListenerInterface() {}
 };
 
+// Pure virtual class to close connection on unrecoverable errors.
+class NET_EXPORT_PRIVATE QuicConnectionCloseDelegateInterface {
+ public:
+  virtual ~QuicConnectionCloseDelegateInterface() {}
+
+  // Called when an unrecoverable error is encountered.
+  virtual void OnUnrecoverableError(QuicErrorCode error,
+                                    const std::string& error_details,
+                                    ConnectionCloseSource source) = 0;
+};
+
 struct NET_EXPORT_PRIVATE AckListenerWrapper {
   AckListenerWrapper(QuicAckListenerInterface* listener,
                      QuicPacketLength data_length);