Roll WebRTC from 563d497e009f to 18523c34b464 (3 revisions)

https://webrtc.googlesource.com/src.git/+log/563d497e009f..18523c34b464

2020-07-08 handellm@webrtc.org Migrate rtc_base to webrtc::Mutex.
2020-07-08 handellm@webrtc.org Migrate modules/desktop_capture and modules/video_capture to webrtc::Mutex.
2020-07-08 handellm@webrtc.org Clarify logging docs.

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/+doc/master/autoroll/README.md

Bug: None
Tbr: webrtc-chromium-sheriffs-robots@google.com
Change-Id: I4382c2f21c9c978372a8a7dfd7639045ae40676c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2289153
Commit-Queue: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Reviewed-by: chromium-autoroll <chromium-autoroll@skia-public.iam.gserviceaccount.com>
Cr-Commit-Position: refs/heads/master@{#786610}

DEPS

@@ -1463,7 +1463,7 @@ deps = {
   },
 
   'src/third_party/webrtc':
-    Var('webrtc_git') + '/src.git' + '@' + '563d497e009ffbcb146ba5937dcf8e6779ff47a2',
+    Var('webrtc_git') + '/src.git' + '@' + '18523c34b464600540b4b1f042d0d5519a5be953',
 
   'src/third_party/libgifcodec':
      Var('skia_git') + '/libgifcodec' + '@'+  Var('libgifcodec_revision'),