Mark middleClickAutoscroll-{drag,event-fired}.html flaky

This patch marks middleClickAutoscroll-{drag,event-fired}.html on Windows:
 * fast/events/middleClickAutoscroll-event-fired.html
 * virtual/mouseevent_fractional/fast/events/middleClickAutoscroll-drag.html
 * virtual/mouseevent_fractional/fast/events/middleClickAutoscroll-event-fired.html
 * virtual/scroll_customization/fast/events/touch/gesture/gesture-scrollbar-touchpad-fling.html
 * virtual/user-activation-v2/fast/events/middleClickAutoscroll-nested-divs-forbidden.html

NOTRY=true
TBR=sahel@chromium.org

Bug: 891155
Change-Id: Iaa6d1054921f3298af37a5023992826b541c82f5
Reviewed-on: https://chromium-review.googlesource.com/c/1322250Reviewed-by: Yoshifumi Inoue <yosin@chromium.org>
Commit-Queue: Yoshifumi Inoue <yosin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605959}

third_party/WebKit/LayoutTests/TestExpectations

@@ -5325,10 +5325,10 @@ crbug.com/806357 [ Linux ] virtual/threaded/fast/events/pointerevents/pinch/poin
 crbug.com/893869 [ Linux Mac ] css3/masking/mask-repeat-space-padding.html [ Failure Pass ]
 
 # Sheriff 2018-10-12
-crbug.com/891155 [ Linux ] virtual/mouseevent_fractional/fast/events/middleClickAutoscroll-drag.html [ Failure Pass ]
-crbug.com/891155 [ Linux ] virtual/mouseevent_fractional/fast/events/middleClickAutoscroll-event-fired.html [ Failure Pass ]
-crbug.com/891155 [ Linux ] virtual/user-activation-v2/fast/events/middleClickAutoscroll-drag.html [ Failure Pass ]
-crbug.com/891155 [ Linux ] virtual/user-activation-v2/fast/events/middleClickAutoscroll-event-fired.html [ Failure Pass ]
+crbug.com/891155 [ Linux Win ] virtual/mouseevent_fractional/fast/events/middleClickAutoscroll-drag.html [ Failure Pass ]
+crbug.com/891155 [ Linux Win ] virtual/mouseevent_fractional/fast/events/middleClickAutoscroll-event-fired.html [ Failure Pass ]
+crbug.com/891155 [ Linux Win ] virtual/user-activation-v2/fast/events/middleClickAutoscroll-drag.html [ Failure Pass ]
+crbug.com/891155 [ Linux Win ] virtual/user-activation-v2/fast/events/middleClickAutoscroll-event-fired.html [ Failure Pass ]
 
 # Sheriff 2018-10-15
 crbug.com/895257 [ Mac ] external/wpt/css/css-fonts/variations/at-font-face-font-matching.html [ Failure Pass ]