Disable flaky test pointerevent_coalesced_events_attributes.html

pointerevent_coalesced_events_attributes.html is flaky on Mac10.13
Tests (dbg).

https://ci.chromium.org/p/chromium/builders/ci/Mac10.13%20Tests%20%28dbg%29

TBR=nzolghadr@chromium.org

Bug: 1015254
Change-Id: Idd8a879393d643d5ea74e93666823acc20be52f0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1867183Reviewed-by: Lan Wei <lanwei@chromium.org>
Commit-Queue: Lan Wei <lanwei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#707414}

third_party/blink/web_tests/TestExpectations

@@ -5770,3 +5770,4 @@ crbug.com/1015187 [ Linux Mac ] virtual/cross-origin-embedder-policy/external/wp
 
 # Sheriff 2019-10-18
 crbug.com/996250 external/wpt/web-nfc/NFCReader_scan_iframe.https.html [ Timeout ]
+crbug.com/1015254 [ Mac ] external/wpt/pointerevents/extension/pointerevent_coalesced_events_attributes.html [ Pass Failure ]

third_party/blink/web_tests/platform/mac-mac10.13/external/wpt/pointerevents/extension/pointerevent_coalesced_events_attributes-expected.txt

-This is a testharness.js-based test.
-PASS touch coalesced events attributes in pointerevents
-PASS touch pointercancel should not have any coalesced events
-PASS touch pointerover should not have any coalesced events
-PASS touch pointerenter should not have any coalesced events
-PASS touch pointerdown should not have any coalesced events
-FAIL touch pointermove should have >2 coalesced events as main thread is busy.
-PASS touch pointermove coalesced events should all be marked as trusted.
-PASS touch time stamps of coalesced events must be ascending.
-PASS touch pointermove coalesced events should all bubbles and cancelable as false.
-PASS touch pointerup should not have any coalesced events
-PASS touch pointerout should not have any coalesced events
-PASS touch pointerleave should not have any coalesced events
-Harness: the test ran to completion.
-