IDL compiler: Update callback interfaces and start testing

Callback interfaces were not being tested, b/c Perl and Python output
were not exactly equal (due to code cleanup in Python that wasn't ported
back to Perl).
Thus the code bitrotted as we've changed the Perl and Python.
This makes the code work again, fixes all discrepencies, and turns the
test on so this doesn't happen in future.

Perl changes are whitespace and comments,
Python and template are mostly cleanup,
but some substantive change ({creation_context}).

BUG=239771

Review URL: https://codereview.chromium.org/54903006

git-svn-id: svn://svn.chromium.org/blink/trunk@161307 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Web Animations CSS: Replace release asserts with debug asserts

Asserts not related to security should not crash a release build if possible.
This patch changes Web Animation asserts to be debug asserts.

BUG=258896

Review URL: https://codereview.chromium.org/57753002

git-svn-id: svn://svn.chromium.org/blink/trunk@161308 bbb929c8-8fbe-4397-9dbb-9b2b20218538