Implement effective overload set algorithm

To implement the overload resolution algorithm, I'm going to first
implement basic algorithms from the spec (*without* changing
generated code), then incrementally switch existing interfaces to
the proper algorithm (changing the generated code).

This implements the "effective overload set" algorithm:
http://heycam.github.io/webidl/#dfn-effective-overload-set

The code isn't very Pythonic, but it's directly from the spec.

Next will be 'distinguishing index'.

R=haraken
BUG=293561

Review URL: https://codereview.chromium.org/274503003

git-svn-id: svn://svn.chromium.org/blink/trunk@173625 bbb929c8-8fbe-4397-9dbb-9b2b20218538