IDL compiler: sync Python to r167411

Python side to:
Rename privateTemplate() and domTemplate()
https://codereview.chromium.org/145843004/

BUG=239771
TBR=haraken
NOTRY=true

Review URL: https://codereview.chromium.org/176833002

git-svn-id: svn://svn.chromium.org/blink/trunk@167653 bbb929c8-8fbe-4397-9dbb-9b2b20218538