Reland "Change ICE connection state on transceiver changes"

This reverts the revert
https://chromium-review.googlesource.com/c/chromium/src/+/1636231
which couldn't be reverted using "reland".

Reason for reland: Flakiness seems to have been caused by leftover
-expect files, not this patch.

TBR=hbos@chromium.org

Bug: chromium:966798
Change-Id: I450908dd3f49a8ae96bec2ba84c2812c40174e9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1635811
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664669}

third_party/blink/renderer/modules/peerconnection/rtc_peer_connection.cc

@@ -2900,6 +2900,15 @@ void RTCPeerConnection::DidModifyTransceivers(
     transceiver->receiver()->track()->Component()->Source()->SetReadyState(
         MediaStreamSource::kReadyStateLive);
   }
+
+  // Transceiver modifications can cause changes in the set of ICE
+  // transports, which may affect ICE transport state.
+  // Note - this must be done every time the set of ICE transports happens.
+  // At the moment this only happens in SLD/SRD, and this function is called
+  // whenever these functions complete.
+  if (sdp_semantics_ == webrtc::SdpSemantics::kUnifiedPlan) {
+    UpdateIceConnectionState();
+  }
 }
 
 void RTCPeerConnection::SetAssociatedMediaStreams(