Render shields before highlighting code

Summary:
It saves some time on non-highlighting generated and other not interesting code.

The code is quite complex (300 lines methods) so I'm not sure if everything is moved correctly.

P.S. I hope that moved code detector will work...

Test Plan:
Display generated file with all whitespace, verify that it is not highlighted.
Display normal file.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Maniphest Tasks: T1134

Differential Revision: https://secure.phabricator.com/D2358