IDL compiler: sync Python to r166688 (and clean up special operations+union code)

IDL compiler: sync Python to r166688 (and clean up special operations+union code)

Python side to:
Update HTMLFormControlsCollection's named getter to behave according to spec
https://codereview.chromium.org/157013006

This also involves lots of cleaning up to special operations and union type code,
making it more generic and avoiding duplication on the Python side.
* Rename collection => imp
* Rename element => result (for union type in/out variables)
* Remove blank lines in nested code

With a bit more cleaning (post-rewrite), special operations can use the
default methods code generation with only minor changes!

BUG=239771
TBR=haraken

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166808

[Nils Barth (inactive), 2014-02-10 06:41:09]

The CQ bit was checked by nbarth@chromium.org

[commit-bot: I haz the power, 2014-02-10 06:41:22]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/nbarth@chromium.org/158663002/20001

[haraken, 2014-02-10 06:56:20]

LGTM

[commit-bot: I haz the power, 2014-02-10 07:59:18]

Change committed as 166808