Re-enable same origin subframe isInputPending WPT

Now that the event wait time has been increased, this test should be less flaky. Re-enable it accordingly.

Bug: 1124978
Change-Id: I221ea9cb96106801d9266e94447660c323ecdd97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2567110Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#832622}

third_party/blink/web_tests/TestExpectations

@@ -5780,9 +5780,6 @@ crbug.com/1122582 external/wpt/html/cross-origin-opener-policy/coop-csp-sandbox-
 # Sheriff 2020-11-20
 crbug.com/1071909 external/wpt/html/cross-origin-opener-policy/popup-coop-by-sw.https.html [ Pass Timeout ]
 
-# Sheriff 2020-09-08
-crbug.com/1124978 [ Mac ] virtual/threaded-composited-iframes/external/wpt/is-input-pending/tentative/same-origin-subframe.sub.html [ Pass Failure ]
-
 # Mac11.0 rebaseline
 crbug.com/1122490 [ Mac11.0 ] virtual/text-antialias/mac-system-ui-weight.html [ Failure ]
 crbug.com/1122490 [ Mac11.0 ] virtual/text-antialias/mac-system-ui-trak.html [ Failure ]