Cleanup constants in IDL compiler + remove conditional constants

Followup to:
Add constants and primitive type readonly attributes to Python IDL compiler
https://codereview.chromium.org/23068032/

This changes formatting and removes support for [Conditional] constants,
as there are none in actual IDLs and Conditional is deprecated.
This makes the code significantly simpler.
Also some minor code factoring changes.

Review URL: https://chromiumcodereview.appspot.com/23455010

git-svn-id: svn://svn.chromium.org/blink/trunk@156778 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Workaround for renderer glitch.

Table renderer ocassionally renders zero-width cells over right border of
perceding cells. This may appear when user hovers cell, or something like that.

If we replace right borders with left borders, then glitch doesn't appear.

BUG=264663

Review URL: https://chromiumcodereview.appspot.com/21087010

git-svn-id: svn://svn.chromium.org/blink/trunk@156779 bbb929c8-8fbe-4397-9dbb-9b2b20218538