Roll src/third_party/webrtc fc8279d66c81..c9f42ad909c0 (4 commits)

https://webrtc.googlesource.com/src.git/+log/fc8279d66c81..c9f42ad909c0

git log fc8279d66c81..c9f42ad909c0 --date=short --first-parent --format='%ad %ae %s'
2020-01-17 srte@webrtc.org Simplifies transport overhead mechanism in Scenario test framework.
2020-01-17 saza@webrtc.org Remove unused AEC delay offset API
2020-01-17 hbos@webrtc.org ResourceAdaptationModule HasInputVideo+DegradationPreference setters.
2020-01-17 peah@webrtc.org Reland "Replace the ExperimentalAgc config with the new config format"

Created with:
  gclient setdep -r src/third_party/webrtc@c9f42ad909c0

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: None
Tbr: webrtc-chromium-sheriffs-robots@google.com
Change-Id: I5157cea9673dd5979c29787204e5678963040bc5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2007591Reviewed-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@{#732852}

DEPS

@@ -1498,7 +1498,7 @@ deps = {
     Var('chromium_git') + '/external/khronosgroup/webgl.git' + '@' + '4f3976e9b368ccfe7b9dd02014351936296dc72c',
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + 'fc8279d66c810eb48e6eaeb9fe83ec447d969292',
+    Var('webrtc_git') + '/src.git' + '@' + 'c9f42ad909c07dc96e56d625cf89cdf5b701364d',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),