Sheriff: Mark external/wpt/webrtc/RTCDTMFSender-ontonechange.https.html as flaky on Mac

Bug: 923244
Change-Id: Ibf8226768c75cde57106ffa3c4ea36cf549b3826
Tbr: nhiroki@chromium.org
Notry: true
Reviewed-on: https://chromium-review.googlesource.com/c/1420513
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Commit-Queue: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624026}
1 file changed