Mojo: fix js bindings

BUG=348080
R=davemoore@chromium.org

Review URL: https://codereview.chromium.org/183273007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254205 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254205