GitLab

Add kill switch for notifications.
Disabled notifications for task manager test.

BUG=286157
NOTRY=true

Review URL: https://chromiumcodereview.appspot.com/23903024

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@222238 0039d316-1c4b-4281-b951-d872f2087c98