Allow fast/peerconnection/RTCRtpSender-setParameters.html to timeout.

The test is flaky. See https://crbug.com/836783.

TBR=orphis@chromium.org

No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 836783
Change-Id: I854823be77f95bed0d562f5f2968064e7342352e
Reviewed-on: https://chromium-review.googlesource.com/1027871Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Henrik Boström <hbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553518}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4141,3 +4141,4 @@ crbug.com/836295 [ Win ] svg/animations/reinserting-svg-into-document.html [ Pas
 
 # Sheriff 2018-04-25
 crbug.com/836763 [ Win7 ] external/wpt/websockets/Create-protocols-repeated-case-insensitive.any.js [ Pass Failure ]
+crbug.com/836783 fast/peerconnection/RTCRtpSender-setParameters.html [ Pass Timeout ]