GitLab

I reused LazyBackgroundTaskQueue so that this works for regular background
pages, which may not be fully loaded by the time this event is dispatched.

BUG=132328


Review URL: https://chromiumcodereview.appspot.com/10828218

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@152017 0039d316-1c4b-4281-b951-d872f2087c98