[Files.app] Hide the CWS token from the drive log

BUG=none
TEST=none
R=hashimoto@chromium.org

Review URL: https://codereview.chromium.org/26443002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227493 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227493