IDL compiler: Move includes to global variable

This refactoring moves includes to a global variable
(use a module to implement Singleton pattern in Python),
which simplifies function calls substantially.

BUG=239771
NOTRY=true

Review URL: https://codereview.chromium.org/38643004

git-svn-id: svn://svn.chromium.org/blink/trunk@160432 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[CSSRegions] -webkit-background-clip: text; does not clip the background in regions

Force black text behavior if flow thread is in the text clip paintint phase.
(Original WebKit patch by Max Vujovic)

Make style checker pass for modified files.

BUG=307047

Review URL: https://codereview.chromium.org/26931005

git-svn-id: svn://svn.chromium.org/blink/trunk@160433 bbb929c8-8fbe-4397-9dbb-9b2b20218538