Mark fast/events/wheel/wheel-latched-scroll-node-removed.html flaky on Mac

See failure here:
https://ci.chromium.org/buildbot/chromium.webkit/WebKit%20Mac10.13%20%28retina%29/1465

TBR=wjmaclean@chromium.org
NOTRY=true

Bug: 869726
Change-Id: Id5e2c77e6c6eb001dbd2c8fcd1b9d5e3df02fb66
Reviewed-on: https://chromium-review.googlesource.com/1176061Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583274}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3919,6 +3919,7 @@ crbug.com/873435 virtual/user-activation-v2/fast/events/middleClickAutoscroll-in
 # Sheriff failures 2018-08-15
 crbug.com/873435 [ Mac ] fast/events/middleClickAutoscroll-in-iframe.html [ Timeout Pass ]
 crbug.com/869726 [ Mac ] fast/events/touch/touch-latched-scroll-node-removed.html [ Pass Failure ]
+crbug.com/869726 [ Mac ] fast/events/wheel/wheel-latched-scroll-node-removed.html [ Pass Failure ]
 crbug.com/874444 [ Linux ] external/wpt/fullscreen/api/element-request-fullscreen-two-elements-manual.html [ Pass Failure ]
 
 crbug.com/715718 external/wpt/media-source/mediasource-activesourcebuffers.html [ Failure Pass ]