Roll src/third_party/webrtc 524417f3f7d0..db6ca7f2d7fd (4 commits)

https://webrtc.googlesource.com/src.git/+log/524417f3f7d0..db6ca7f2d7fd

git log 524417f3f7d0..db6ca7f2d7fd --date=short --first-parent --format='%ad %ae %s'
2020-01-17 ilnik@webrtc.org Add safety checks in RtpPacket::ZeroMutableExtensions and fuzz it
2020-01-17 srte@webrtc.org Do not allow sending tasks to a thread that is quitting.
2020-01-17 phoglund@webrtc.org Repurpose upload script to read natively generated histogram json.
2020-01-17 srte@webrtc.org Using EmulatedEndpoint in Scenario tests.

Created with:
  gclient setdep -r src/third_party/webrtc@db6ca7f2d7fd

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:1042535
Tbr: webrtc-chromium-sheriffs-robots@google.com
Change-Id: I4eb4791a8a50d8fedbb5ee2c497787a882fc73e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2007911Reviewed-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@{#732896}

DEPS

@@ -1498,7 +1498,7 @@ deps = {
     Var('chromium_git') + '/external/khronosgroup/webgl.git' + '@' + '4f3976e9b368ccfe7b9dd02014351936296dc72c',
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '524417f3f7d0e3b1da4866db74221cd769bdd4bb',
+    Var('webrtc_git') + '/src.git' + '@' + 'db6ca7f2d7fd67b2ed37b49af442ff58171faafa',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),