Roll src/third_party/webrtc 29cf2b0cbb75..1261b5caa386 (3 commits)

https://webrtc.googlesource.com/src.git/+log/29cf2b0cbb75..1261b5caa386

git log 29cf2b0cbb75..1261b5caa386 --date=short --first-parent --format='%ad %ae %s'
2020-04-17 hbos@webrtc.org [Adaptation] Move EffectiveDegradationPreference to RA-Processor.
2020-04-17 mbonadei@webrtc.org Remove WebRTC-LibvpxVp{8,9}TrustedRateController.
2020-04-17 hbos@webrtc.org [Adaptation] Delete Processor Proof-of-Concept.

Created with:
  gclient setdep -r src/third_party/webrtc@1261b5caa386

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: If8a47c59b7a424f7d9d123b9a415cc790c98fe6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2154553Reviewed-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@{#760034}

DEPS

@@ -1447,7 +1447,7 @@ deps = {
   },
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '29cf2b0cbb75abcceecdb2488c3cec0719b65160',
+    Var('webrtc_git') + '/src.git' + '@' + '1261b5caa38688778036411fca513548efd10e31',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),