Increase event wait time for isInputPending WPTs

To reduce flakiness of positive isInputPending tests, wait for 500ms rather
than 200ms in an attempt to mitigate queueing delay variance.

Bug: 910421, 1124978, 1126853
Change-Id: I3136cdc0941b427c97c15de8969d7bbe243b4218
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2415137
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#807693}

is-input-pending/resources/input-onmessage.js

@@ -7,7 +7,7 @@ onmessage = async e => {
 
   // Use a reasonable time to wait after dispatching events, since we want to be
   // able to test for cases where isInputPending returns false.
-  const DISPATCH_WAIT_TIME_MS = 200;
+  const DISPATCH_WAIT_TIME_MS = 500;
 
   // Wait a reasonable amount of time for the event to be enqueued.
   const end = performance.now() + DISPATCH_WAIT_TIME_MS;