Added wpt test to ensure no gathering state change.

Depends on D93310

Differential Revision: https://phabricator.services.mozilla.com/D94123

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1670856
gecko-commit: 9e4bc6105c62b6ee012e52ba2720d55ea11cf764
gecko-reviewers: bwc

webrtc/RTCPeerConnection-iceGatheringState.html

@@ -101,6 +101,17 @@
     await new Promise(r => t.step_timeout(r, 500));
   }, 'setLocalDescription(reoffer) with no new transports should not cause iceGatheringState to change');
 
+  promise_test(async t => {
+    const pc1 = new RTCPeerConnection();
+    t.add_cleanup(() => pc1.close());
+
+    expectNoMoreGatheringStateChanges(t, pc1);
+
+    await pc1.setLocalDescription(await pc1.createOffer());
+
+    await new Promise(r => t.step_timeout(r, 500));
+  }, 'setLocalDescription() with no transports should not cause iceGatheringState to change');
+
   promise_test(async t => {
     const pc1 = new RTCPeerConnection();
     t.add_cleanup(() => pc1.close());