Mark flaky on Mac10.13: .../gamepad/multiple-event-listeners.html.

TBR=scottmg@chromium.org

Bug: 907862
Change-Id: I3fa8fbb2e75b4744cf47031f233bfd4ce613a38d
Reviewed-on: https://chromium-review.googlesource.com/c/1348056Reviewed-by: Anders Hartvoll Ruud <andruud@chromium.org>
Commit-Queue: Anders Hartvoll Ruud <andruud@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610400}

third_party/WebKit/LayoutTests/TestExpectations

@@ -5406,3 +5406,4 @@ crbug.com/907481 [ Win10 ] virtual/webrtc-wpt-unified-plan/external/wpt/webrtc/R
 
 #Sheriff 2018-11-22
 crbug.com/907736 http/tests/devtools/elements/elements-save-to-temp-var.js [ Timeout Pass ]
+crbug.com/907862 [ Mac10.13 ] virtual/user-activation-v2/gamepad/multiple-event-listeners.html [ Pass Failure ]