Do not preprend app_list:: when it isn't necessary.

Idealy this should be added to PRESUMIT like it's being done
in https://codereview.chromium.org/109263003/.

BUG=None
TEST=app_list_unittests
TBR=xiyuan@chromium.org

Review URL: https://codereview.chromium.org/109783002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239427 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239427