It doesn't need to use a traverser, since all function definitions can
be found simply by iterating over the children of the root node.

BUG=angleproject:2040
TEST=angle_unittests

Change-Id: I18a98eff9710485c0cdce73e7fffe124f7d7afb2
Reviewed-on: https://chromium-review.googlesource.com/508791Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>