Removes an assert on the WorkerThread's worker global scope ref count.
Removes an assert on the WorkerThread's worker global scope ref count.

This is in preparation for http://crrev.com/1209403005.

BUG=

Review URL: https://codereview.chromium.org/1224173005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@198796 bbb929c8-8fbe-4397-9dbb-9b2b20218538

Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk