Remove the check for task events, as they were all flow events

All the MessageLoop::PostTask: were of the category task, and in this test were all flow events (81 counts)
Flow events have been disabled-by-default (crbug/338427), the count became 0 --> removing the check.

BUG=341641

Review URL: https://codereview.chromium.org/133313006

git-svn-id: svn://svn.chromium.org/blink/trunk@166729 bbb929c8-8fbe-4397-9dbb-9b2b20218538