Roll src/third_party/webrtc b6685420c42a..b1686786e896 (2 commits)

https://webrtc.googlesource.com/src.git/+log/b6685420c42a..b1686786e896

git log b6685420c42a..b1686786e896 --date=short --no-merges --format='%ad %ae %s'
2019-08-07 oprypin@webrtc.org Add RTC_ prefix to non-standard format specifier macro "PRIdNS"
2019-08-07 nisse@webrtc.org Delete RtcpStatisticsCallback from ReceiveStatistics

Created with:
  gclient setdep -r src/third_party/webrtc@b1686786e896

The AutoRoll server is located here: https://autoroll.skia.org/r/webrtc-chromium-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.


TBR=webrtc-chromium-sheriffs-robots@google.com

Bug: None
Change-Id: I50027f2298a39c460b2bc89d458af45c5dd7d003
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1742387
Reviewed-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@{#684799}