IDL build: factor out interface_info actions into GYP templates

Followup to:
IDL build: factor out global constructors action into a GYP template
https://codereview.chromium.org/319933002/

R=haraken

Review URL: https://codereview.chromium.org/328643002

git-svn-id: svn://svn.chromium.org/blink/trunk@176091 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Turn conditionals back on in aggregate bindings

Aggregate bindings are supposed to wrap the include of
interfaces that have [Conditional] on their definition with
ifdef, so these are not compiled if these are turned off.

However, this was broken so it didn't work,
and we couldn't turn it on, due to linking failure in SVG.
(I noticed this during a cleanup.)

This now can be turned back on, perhaps thanks to Kouhei's
fix-up of SVG bindings (or something Mahesh has been doing?).
Turning it on thus speeds up and simplifies compilation
somewhat.

(The only [Conditional] compilation flags on interfaces
are SVG_FONTS and WEB_AUDIO.)

I looked into this because of Mahesh's other Conditional fixes in:
Add support in generate scripts to handle Conditional
https://codereview.chromium.org/330093002/

R=haraken

Review URL: https://codereview.chromium.org/333803003

git-svn-id: svn://svn.chromium.org/blink/trunk@176092 bbb929c8-8fbe-4397-9dbb-9b2b20218538