BUG=angleproject:1158 part a

We only need to iterate and update the active attributes in a program.
This can further be optimized by updating the cache more intelligently,
possibly by marking attributes as "need update" when necessary

Change-Id: I41e9c033116582c82a56b8d20ea245f06e8fa3d1
Reviewed-on: https://chromium-review.googlesource.com/299758Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tryjob-Request: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>