Files.app: Update availability of OK button by using input events.
Previously the availability is updated by handling keydown events. But when the
events are published, the input value has not updated yet. This CL turns the
events handled to update the availability into input events.
BUG=326094
TEST=Open save file dialog, input and delete text in the filename input.
Review URL: https://codereview.chromium.org/
108013003
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239212 0039d316-1c4b-4281-b951-d872f2087c98