Add two versions of the test - one with a single pow(), and another with
a nested pow().

TEST=angle_unittests
BUG=477306

Change-Id: Idb38e57a4b2522b7794996d6ea0f0456b349abf7
Reviewed-on: https://chromium-review.googlesource.com/274736Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>