Roll WebRTC from 4b18e249672f to af704183574c (5 revisions)

https://webrtc.googlesource.com/src.git/+log/4b18e249672f..af704183574c

2020-10-19 perkj@webrtc.org Hookup VideoSendStreamImpl::OnVideoLayersAllocationUpdate to RtpVideoSender.
2020-10-19 chromium-webrtc-autoroll@webrtc-ci.iam.gserviceaccount.com Roll chromium_revision f16d83f8..cb51eef7 (818270:818409)
2020-10-19 danilchap@webrtc.org Allow to set av1 scalability mode after encoder is constructed
2020-10-19 perkj@webrtc.org Make sprang@ owner in call
2020-10-19 hta@webrtc.org IWYU: Don't filter for already-included header files.

If this roll has caused a breakage, revert this CL and stop the roller
using the controls here:
https://autoroll.skia.org/r/webrtc-chromium-autoroll
Please CC webrtc-chromium-sheriffs-robots@google.com on the revert to ensure that a human
is aware of the problem.

To report a problem with the AutoRoller itself, please file a bug:
https://bugs.chromium.org/p/skia/issues/entry?template=Autoroller+Bug

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+doc/master/autoroll/README.md

Bug: None
Tbr: webrtc-chromium-sheriffs-robots@google.com
Change-Id: I082efc3177336fd2dcd0629360a8bd3755b32381
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2484154Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#818492}

DEPS

@@ -1497,7 +1497,7 @@ deps = {
   },
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '4b18e249672fee9ea79c59f8b0d9bdb9984bc228',
+    Var('webrtc_git') + '/src.git' + '@' + 'af704183574c9b6540bd7dee27ba779950509f31',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),