IDL compiler: sync Python to r162830 (part 2)

Followup to:
IDL compiler: sync Python to r162830
https://codereview.chromium.org/98073002/

Remaining syncs to:
Remove usage of deprecated V8 APIs from bindings code generator
https://codereview.chromium.org/94833002

BUG=239771
NOTRY=true
TBR=haraken

Review URL: https://codereview.chromium.org/98053003

git-svn-id: svn://svn.chromium.org/blink/trunk@162946 bbb929c8-8fbe-4397-9dbb-9b2b20218538