Roll src/third_party/webrtc 1242d9cc48ca..c5ec54e51b91 (3 commits)

https://webrtc.googlesource.com/src.git/+log/1242d9cc48ca..c5ec54e51b91

git log 1242d9cc48ca..c5ec54e51b91 --date=short --no-merges --format='%ad %ae %s'
2019-11-13 jakobi@webrtc.org Add SetIsScreencast method to VideoSource.
2019-11-13 mbonadei@webrtc.org Revert "Reland "Define WEBRTC_ENABLE_SYMBOL_EXPORT if is_component_build=true.""
2019-11-13 mbonadei@webrtc.org Reland "Define WEBRTC_ENABLE_SYMBOL_EXPORT if is_component_build=true."

Created with:
  gclient setdep -r src/third_party/webrtc@c5ec54e51b91

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:None
Change-Id: Ie07ac445e45e1ec62a86519bf9cd2d45cd499060
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1914285Reviewed-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@{#714912}

DEPS

@@ -1484,7 +1484,7 @@ deps = {
     Var('chromium_git') + '/external/khronosgroup/webgl.git' + '@' + 'dd55f3ca8f2ea716ca917a4aaf36f0729fe902b1',
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '1242d9cc48caff9bb292f40f374d1b6f1ab1f814',
+    Var('webrtc_git') + '/src.git' + '@' + 'c5ec54e51b91c2b676614fccc7135afe8e123946',
 
   # 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.