[Sheriff] Mark v/c/f/s/s/scrollbar-button-gesture-target.html flaky.

Mark
virtual/compositor_threaded_scrollbar_scrolling/fast/scrolling/scrollbars/scrollbar-button-gesture-target.html
as flaky (crash) on Win.

TBR=arakeri@microsoft.com

Bug: 987115
Change-Id: I95eeddd53240a6921b5dec33b7481bb7bbe5232e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1728658Reviewed-by: vitaliii <vitaliii@chromium.org>
Commit-Queue: vitaliii <vitaliii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682666}

third_party/blink/web_tests/TestExpectations

@@ -3212,7 +3212,8 @@ crbug.com/953847 [ Mac ] virtual/main_thread_scrollbar_gestures/fast/scrolling/s
 # Note: even when fixed will still fail on Mac until crbug.com/953847
 # is addressed. Uncomment below line when fixing crbug.com/965829.
 #crbug.com/953847 [ Mac ] virtual/compositor_threaded_scrollbar_scrolling/fast/scrolling/scrollbars/scrollbar-button-gesture-target.html [ Failure ]
-crbug.com/965829 virtual/compositor_threaded_scrollbar_scrolling/fast/scrolling/scrollbars/scrollbar-button-gesture-target.html [ Failure ]
+crbug.com/987115 [ Win ] virtual/compositor_threaded_scrollbar_scrolling/fast/scrolling/scrollbars/scrollbar-button-gesture-target.html [ Failure Crash ]
+crbug.com/965829 [ Mac Linux ] virtual/compositor_threaded_scrollbar_scrolling/fast/scrolling/scrollbars/scrollbar-button-gesture-target.html [ Failure ]
 
 # Some control characters still not visible
 crbug.com/893490 [ Mac ] external/wpt/css/css-text/white-space/control-chars-001.html [ Failure ]