Fixed a runtime error caused by incomplete manifestTypes in _api_features.json

BUG=302841
R=kalman@chromium.org

Review URL: https://codereview.chromium.org/25650002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226498 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226498