Add a flag to show if the FileChooserCompletion needs local paths or not.

BUG=126902
TEST=None

Review URL: https://codereview.chromium.org/637873006

git-svn-id: svn://svn.chromium.org/blink/trunk@183798 bbb929c8-8fbe-4397-9dbb-9b2b20218538