Add timeout to an existing flaky test.

This test is already flaky and now also times out. Importer tries to add
the timeout as a separate line instead of combining it with the existing
line, which causes a lint error.

TBR=smcgruer

Change-Id: I0046597b917746e5ec8e7110025f1507adf74582
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391205Reviewed-by: Luke Z <lpz@chromium.org>
Reviewed-by: Stephen McGruer <smcgruer@chromium.org>
Commit-Queue: Luke Z <lpz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804360}

third_party/blink/web_tests/TestExpectations

@@ -2546,7 +2546,7 @@ crbug.com/1105958 external/wpt/payment-request/payment-is-showing.https.html [ T
 crbug.com/626703 external/wpt/css/css-pseudo/file-selector-button-001.tentative.html [ Failure ]
 crbug.com/626703 [ Mac10.13 ] external/wpt/pointerevents/compat/pointerevent_mouse-pointer-preventdefault.html [ Timeout Pass Failure ]
 crbug.com/626703 [ Mac10.14 ] external/wpt/pointerevents/compat/pointerevent_mouse-pointer-preventdefault.html [ Timeout ]
-crbug.com/626703 [ Mac10.15 ] external/wpt/pointerevents/compat/pointerevent_mouse-pointer-preventdefault.html [ Pass Failure ]
+crbug.com/626703 [ Mac10.15 ] external/wpt/pointerevents/compat/pointerevent_mouse-pointer-preventdefault.html [ Timeout Pass Failure ]
 crbug.com/626703 [ Mac10.15 ] virtual/threaded/external/wpt/animation-worklet/worklet-animation-with-scroll-timeline-root-scroller.https.html [ Failure ]
 crbug.com/626703 [ Mac10.14 ] virtual/off-main-thread-css-paint/external/wpt/css/css-paint-api/valid-image-before-load.https.html [ Failure ]
 crbug.com/626703 external/wpt/web-share/share-url-invalid.https.html [ Crash ]