DevTools: Coalesce orphan invokeOnceAfterBatchUpdate tasks

Coalesce invokeOnceAfterBatchUpdate tasks fired outside of
start/end batches.

Review URL: https://codereview.chromium.org/225763003

git-svn-id: svn://svn.chromium.org/blink/trunk@171051 bbb929c8-8fbe-4397-9dbb-9b2b20218538