Fix Chromium FYI bot breakage caused by ICE interface change

webrtc/p2p/base/mockicetransport.h

Index: webrtc/p2p/base/mockicetransport.h
diff --git a/webrtc/p2p/base/mockicetransport.h b/webrtc/p2p/base/mockicetransport.h
index 0499c9f8b6541aaf50720255417dddc44f6b45d4..53549abe86d1d1e2c1af98c12f9b34a751adaad3 100644
--- a/webrtc/p2p/base/mockicetransport.h
+++ b/webrtc/p2p/base/mockicetransport.h
@@ -57,6 +57,9 @@ class MockIceTransport : public IceTransportInternal {
   void SetRemoteIceParameters(const IceParameters& ice_params) override {}
   void SetRemoteIceMode(IceMode mode) override {}
   void SetIceConfig(const IceConfig& config) override {}
+  rtc::Optional<int> GetRttEstimate() override {
+    return rtc::Optional<int>();
+  }
   void MaybeStartGathering() override {}
   void SetMetricsObserver(webrtc::MetricsObserverInterface* observer) override {
   }