Roll src/third_party/webrtc 78c7c5247c3e..ef0d76ae836b (2 commits)

https://webrtc.googlesource.com/src.git/+log/78c7c5247c3e..ef0d76ae836b

git log 78c7c5247c3e..ef0d76ae836b --date=short --first-parent --format='%ad %ae %s'
2020-02-06 ilnik@webrtc.org Add more VP9 header correctness check in RtpFrameReferenceFinder
2020-02-06 eshr@google.com Move quality rampup experiment to overuse module

Created with:
  gclient setdep -r src/third_party/webrtc@ef0d76ae836b

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:1049129
Tbr: webrtc-chromium-sheriffs-robots@google.com
Change-Id: I3492c44a781e99e9941ab1dcbf83edea22a239d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2041326Reviewed-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@{#738923}

DEPS

@@ -1458,7 +1458,7 @@ deps = {
     Var('chromium_git') + '/external/github.com/gpuweb/cts.git' + '@' + 'ec18cc3262922e7dcdbe70243c6f40606f979144',
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '78c7c5247c3e6a23580d3a68f13db8bec1bc53bd',
+    Var('webrtc_git') + '/src.git' + '@' + 'ef0d76ae836bf0370065fc7e1858301aa47ef1df',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),