Roll WebRTC from d40c764ba81e to e15fb15035fe (3 revisions)

https://webrtc.googlesource.com/src.git/+log/d40c764ba81e..e15fb15035fe

2020-10-19 hta@webrtc.org Separate RTP object handling (senders, receivers, transceivers)
2020-10-19 danilchap@webrtc.org Support layer skipping in S2T1 structure
2020-10-19 olka@webrtc.org Move dynamic memory allocations of webrtc::AudioMixerImpl from RT thead

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: I59004c693a3ac397ac438e995e27bdaf6b6826a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2486053Reviewed-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@{#818638}

DEPS

@@ -1497,7 +1497,7 @@ deps = {
   },
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + 'd40c764ba81e24883b8c79ffa257c1eacab50fc7',
+    Var('webrtc_git') + '/src.git' + '@' + 'e15fb15035fe5391a95a32a3d26cd611302ed688',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),