Roll src/third_party/webrtc/ 6dfc8d6ef..4478d9b77 (9 commits)

https://webrtc.googlesource.com/src.git/+log/6dfc8d6ef3b2..4478d9b7733d

$ git log 6dfc8d6ef..4478d9b77 --date=short --no-merges --format='%ad %ae %s'

Created with:
  roll-dep src/third_party/webrtc
BUG=chromium:None,chromium:None


The AutoRoll server is located here: https://webrtc-chromium-roll.skia.org

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

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.


CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_chromium_archive_rel_ng;master.tryserver.chromium.mac:mac_chromium_archive_rel_ng
TBR=webrtc-chromium-sheriffs-robots@google.com

Change-Id: I0c840e576be99c817a3a422bace6b58d7eb6d749
Reviewed-on: https://chromium-review.googlesource.com/1014952Reviewed-by: webrtc-chromium-autoroll <webrtc-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Commit-Queue: webrtc-chromium-autoroll <webrtc-chromium-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#551440}

DEPS

@@ -950,7 +950,7 @@ deps = {
     Var('chromium_git') + '/external/khronosgroup/webgl.git' + '@' + '7c0541da63f571512c49758cbc0767117997a270',
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '6dfc8d6ef3b21bce28a501cc6fb6d09754ddf5af', # commit position 21742
+    Var('webrtc_git') + '/src.git' + '@' + '4478d9b7733de49973f42a35fc47374d570a47c3', # commit position 21742
 
   'src/third_party/xdg-utils': {
       'url': Var('chromium_git') + '/chromium/deps/xdg-utils.git' + '@' + 'd80274d5869b17b8c9067a1022e4416ee7ed5e0d',