Roll src/third_party/webrtc 470b2d5144a3..4778f6ce7a0b (3 commits)

https://webrtc.googlesource.com/src.git/+log/470b2d5144a3..4778f6ce7a0b

git log 470b2d5144a3..4778f6ce7a0b --date=short --no-merges --format='%ad %ae %s'
2019-10-30 titovartem@webrtc.org Revert "Refactoring of the noise suppressor and adding true multichannel support"
2019-10-30 sakal@webrtc.org Fix invalid @Nullable handling in TextureBufferImpl.
2019-10-30 srte@webrtc.org Cleanup of feedback observer interface

Created with:
  gclient setdep -r src/third_party/webrtc@4778f6ce7a0b

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

TBR=webrtc-chromium-sheriffs-robots@google.com

Bug: chromium:b/143344262,chromium:None
Change-Id: Ic24032eacfc8b8c4765051190e7bcde50566ca74
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1890212Reviewed-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@{#710752}

DEPS

@@ -1507,7 +1507,7 @@ deps = {
     Var('chromium_git') + '/external/khronosgroup/webgl.git' + '@' + '2701c130839edbeb226735b0775966b6423d9e83',
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '470b2d5144a3a00ed82b017ede000098fb39df6b',
+    Var('webrtc_git') + '/src.git' + '@' + '4778f6ce7a0b0b3c660c87d895904521a5f41d5a',
 
   # Wuffs' canonical repository is at github.com/google/wuffs, but we use
   # Skia's mirror of Wuffs, the same as in upstream Skia's DEPS file.