Log the dtls handshake error.

content/renderer/media/rtc_peer_connection_handler.cc

Index: content/renderer/media/rtc_peer_connection_handler.cc
diff --git a/content/renderer/media/rtc_peer_connection_handler.cc b/content/renderer/media/rtc_peer_connection_handler.cc
index 8112398d99df84698bc77891573e1fc3e79a9774..d4cf78c6f6b193cf96ada793c3ec156dda0711c5 100644
--- a/content/renderer/media/rtc_peer_connection_handler.cc
+++ b/content/renderer/media/rtc_peer_connection_handler.cc
@@ -710,6 +710,10 @@ class PeerConnectionUMAObserver : public webrtc::UMAObserver {
         UMA_HISTOGRAM_ENUMERATION("WebRTC.PeerConnection.CandidatePairType_TCP",
                                   counter, counter_max);
         break;
+      case webrtc::kEnumCounterDtlsHandshakeError:
+        UMA_HISTOGRAM_ENUMERATION("WebRTC.PeerConnection.DtlsHandshakeError",
+                                  counter, counter_max);
+        break;
       default:
         // The default clause is expected to reach when new enum types are
         // added.