IDL compiler: sync Python to r162776

Python side to:
Make IDL Callbacks non-refcounted by default
https://codereview.chromium.org/85263006

Slightly more involved than other syncs
(new logic, not just changing content).
This finishes the syncing to last week's Perl changes.

BUG=239771
BUG=323681
NOTRY=true

Review URL: https://codereview.chromium.org/98173002

git-svn-id: svn://svn.chromium.org/blink/trunk@162947 bbb929c8-8fbe-4397-9dbb-9b2b20218538