Check that scalabilityMode is present in sender parameters

Bug: none
Change-Id: If011bd5d963b3362c62b2205e2e8a0c95898e7f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3240743
Reviewed-by: Philipp Hancke <philipp.hancke@googlemail.com>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Cr-Commit-Position: refs/heads/main@{#934501}

webrtc-svc/RTCRtpParameters-scalability.html

@@ -5,7 +5,7 @@
 <script src="/resources/testharnessreport.js"></script>
 <script src="/webrtc/dictionary-helper.js"></script>
 <script src="/webrtc/RTCRtpParameters-helper.js"></script>
-<script src="/webrtc/RTCPeerConnection-helper.js"></script>
+<script src="../webrtc/RTCPeerConnection-helper.js"></script>
 <script>
   'use strict';
 
@@ -45,6 +45,8 @@
           v.srcObject = new MediaStream([(await haveTrackEvent).track]);
           await new Promise(r => v.onloadedmetadata = r);
           await detectSignal(t, v, 100);
+          const sendParams = pc1.getSenders()[0].getParameters();
+          assert_equals(sendParams.encodings[0].scalabilityMode, scalabilityMode);
         }, `[${index++}] ${codec.mimeType} - ${scalabilityMode} should produce valid video content`);
       }
     }