Common functionality across some perf tests is moved to a separate
utility file, draw_call_perf_utils.

This will make it simpler to add more perf tests, such as tests for
multiview drawing.

BUG=angleproject:1669
TEST=angle_perftests

Change-Id: I2108d7425f7d8f43f333ea9daa6779e42862350b
Reviewed-on: https://chromium-review.googlesource.com/422332
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>