Patch up checklicenses.py to workaround regression in r244886.

swarming/client DEPS roll introduced two new third parties, httplib2 and
oauth2client.

BUG=334668
R=vadimsh@chromium.org
TBR=phajdan.jr@chromium.org, vadimsh@chromium.org

Review URL: https://codereview.chromium.org/134313008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244892 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244892