Files that only have a single function should be named consistently
with the function. Unnecessary include in CallDAG.h is removed.

BUG=angleproject:2068
TEST=angle_unittests

Change-Id: I27d55a766b9eb66fcfd1e0a2341a2843bb9dc5bb
Reviewed-on: https://chromium-review.googlesource.com/608368
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>