Add UMA metrics for ICE regathering reasons.

webrtc/p2p/base/p2ptransportchannel.cc

Index: webrtc/p2p/base/p2ptransportchannel.cc
diff --git a/webrtc/p2p/base/p2ptransportchannel.cc b/webrtc/p2p/base/p2ptransportchannel.cc
index 3f68d6d6e078fd635e8f696b3b46ae12bae8ce67..6aeac99a75ef4ea39fdbe46a896e4251d67d713d 100644
--- a/webrtc/p2p/base/p2ptransportchannel.cc
+++ b/webrtc/p2p/base/p2ptransportchannel.cc
@@ -451,6 +451,19 @@ void P2PTransportChannel::MaybeStartGathering() {
       gathering_state_ = kIceGatheringGathering;
       SignalGatheringState(this);
     }
+
+    if (!allocator_sessions_.empty()) {
+      IceRegatheringReason reason;
+      if (writable()) {
+        reason = IceRegatheringReason::ICE_RESTART_WHEN_CONNECTED;
+      } else if (IsGettingPorts()) {
+        reason = IceRegatheringReason::ICE_RESTART_WHEN_CONNECTING;
+      } else {
+        reason = IceRegatheringReason::ICE_RESTART_WHEN_DISCONNECTED;
+      }
+      allocator_->ReportIceRegatheringReason(reason);
+    }
+
     // Time for a new allocator.
     std::unique_ptr<PortAllocatorSession> pooled_session =
         allocator_->TakePooledSession(transport_name(), component(),
@@ -473,7 +486,6 @@ void P2PTransportChannel::MaybeStartGathering() {
       AddAllocatorSession(allocator_->CreateSession(
           transport_name(), component(), ice_parameters_.ufrag,
           ice_parameters_.pwd));
-      LOG(LS_INFO) << "Start getting ports";
       allocator_sessions_.back()->StartGettingPorts();
     }
   }