Fix a race in WorkerThreadTicker test.
Fix a race in WorkerThreadTicker test.

TEST=none
BUG=30582

Review URL: http://codereview.chromium.org/506073

git-svn-id: dd90618784b6a4b323ea0c23a071cb1c9e6f2ac7@35378 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser,wistoch/meego-app-browser