This simplifies code and ensures that nodes get consistent data.

In the future function call nodes could have a pointer to the
TFunction instead of converting the same information into a different
data structure.

BUG=angleproject:2267
TEST=angle_unittests, angle_end2end_tests

Change-Id: Ic0c24bb86b44b9bcc4a5da7f6b03701081a3af5c
Reviewed-on: https://chromium-review.googlesource.com/824606Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>