Reland "Change ICE connection state on transceiver changes"

This reverts commit 2229f484.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Revert "Change ICE connection state on transceiver changes"
> 
> This reverts commit 0882bebe.
> 
> Reason for revert: Causing flaky failures of
> external/wpt/webrtc/RTCPeerConnection-iceConnectionState.https.html
> on Linux Tests and WebKit Linux Trusty Leak
> 
> https://ci.chromium.org/p/chromium/builders/ci/Linux%20Tests/78387
> https://ci.chromium.org/p/chromium/builders/ci/WebKit%20Linux%20Trusty%20Leak/34892
> 
> Original change's description:
> > Change ICE connection state on transceiver changes
> > 
> > This ensures that if the PC iceConnectionState should change
> > because unused transports are discarded, the state is updated.
> > 
> > Bug: chromium:966798
> > 
> > Change-Id: I09d945f5e70eec813f33c3131fbe889825613652
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632254
> > Reviewed-by: Henrik Boström <hbos@chromium.org>
> > Commit-Queue: Harald Alvestrand <hta@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#664206}
> 
> TBR=hta@chromium.org,hbos@chromium.org
> 
> Change-Id: I2cbae9f1327e7aacb7022d2a823ce1e954c91b62
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: chromium:966798
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1635208
> Reviewed-by: Aaron Gable <agable@chromium.org>
> Commit-Queue: Aaron Gable <agable@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#664388}

TBR=agable@chromium.org,hta@chromium.org,hbos@chromium.org

Change-Id: I894d30a0c585245b095c27cee9d5eadaf4569654
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:966798
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1635512Reviewed-by: Harald Alvestrand <hta@chromium.org>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#664422}

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

@@ -2899,6 +2899,15 @@ 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(