Roll src/third_party/webrtc 78964c1e0afa..4d3f93f34813 (4 commits)

https://webrtc.googlesource.com/src.git/+log/78964c1e0afa..4d3f93f34813

git log 78964c1e0afa..4d3f93f34813 --date=short --first-parent --format='%ad %ae %s'
2020-03-11 chromium-webrtc-autoroll@webrtc-ci.iam.gserviceaccount.com Roll chromium_revision 9a91e044..03913e7d (749020:749124)
2020-03-11 titovartem@webrtc.org Add jitterBufferTargetDelay as RTCNonStandardStatsMember to new GetStats API
2020-03-11 danilchap@webrtc.org Add Av1 Decoder wrapper behind a build flag
2020-03-11 handellm@webrtc.org RtpTransceiver: add kStopped enumeration value.

Created with:
  gclient setdep -r src/third_party/webrtc@4d3f93f34813

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/+/master/autoroll/README.md

Bug: chromium:980879
Tbr: webrtc-chromium-sheriffs-robots@google.com
Change-Id: I2ff9e0cb5469955468eaa4f6a8f8ed459314db46
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2098235Reviewed-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@{#749210}

DEPS

@@ -1454,7 +1454,7 @@ deps = {
     Var('chromium_git') + '/external/github.com/gpuweb/cts.git' + '@' + 'ec18cc3262922e7dcdbe70243c6f40606f979144',
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '78964c1e0afa60d8e628f4cac304ae550ee92490',
+    Var('webrtc_git') + '/src.git' + '@' + '4d3f93f348136b6cbad827124be4cedf5794aab3',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),