Add UMA metrics for ICE regathering reasons.

webrtc/api/fakemetricsobserver.cc

 /*
  *  Copyright 2015 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 27 matching lines @@
 void FakeMetricsObserver::AddHistogramSample(PeerConnectionMetricsName type,
     int value) {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
   RTC_DCHECK_EQ(histogram_samples_[type], 0);
   histogram_samples_[type] = value;
 }
 
 int FakeMetricsObserver::GetEnumCounter(PeerConnectionEnumCounterType type,
                                         int counter) const {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
-  RTC_CHECK(counters_.size() > static_cast<size_t>(type));
+  if (counters_.size() <= static_cast<size_t>(type)) {
+    return 0;
+  }
   const auto& it = counters_[type].find(counter);
   if (it == counters_[type].end()) {
     return 0;
   }
   return it->second;
 }
 
 int FakeMetricsObserver::GetHistogramSample(
     PeerConnectionMetricsName type) const {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
   return histogram_samples_[type];
 }
 
 }  // namespace webrtc