Roll WebRTC from 0ee4ee85ddf2 to a4d70a802cf7 (3 revisions)

https://webrtc.googlesource.com/src.git/+log/0ee4ee85ddf2..a4d70a802cf7

2020-05-28 danilchap@webrtc.org Configure libaom encoder with scalability parameters
2020-05-28 handellm@webrtc.org Deprecate SignalThread.
2020-05-27 terelius@webrtc.org Replace inconsistent log_segments() function in RTC event log parser

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: Ie7ea42324bc52c1ce6b5e9e7dc2ee1ad39525dfa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2219907Reviewed-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@{#772652}

DEPS

@@ -1453,7 +1453,7 @@ deps = {
   },
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '0ee4ee85ddf21c72592b2027e309161d8fe25a9e',
+    Var('webrtc_git') + '/src.git' + '@' + 'a4d70a802cf7444cb84e87813992a8613cf1037c',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),