Exclude Task Manager strings when enable_task_manager==0.

BUG=326023

Review URL: https://codereview.chromium.org/149463005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247933 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247933