Allow TransportController to create a QuicTransportChannel

webrtc/base/sslfingerprint.h

 /*
  *  Copyright 2012 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 23 matching lines @@
   SSLFingerprint(const std::string& algorithm,
                  const uint8_t* digest_in,
                  size_t digest_len);
 
   SSLFingerprint(const SSLFingerprint& from);
 
   bool operator==(const SSLFingerprint& other) const;
 
   std::string GetRfc4572Fingerprint() const;
 
-  std::string ToString();
+  std::string ToString() const;
 
   std::string algorithm;
   rtc::CopyOnWriteBuffer digest;
 };
 
 }  // namespace rtc
 
 #endif  // WEBRTC_BASE_SSLFINGERPRINT_H_