Fix code style in perf tests 1) Format switch/case with git cl format 2) Change NULL -> nullptr 3) Change int to GLint where appropriate 4) Use more appropriate variants of asserts BUG=angleproject:1261 TEST=angle_perftests Change-Id: I97d6260dbd72ef3897fff145682b7043bf323b76 Reviewed-on: https://chromium-review.googlesource.com/319380 Tryjob-Request: Olli Etuaho <oetuaho@nvidia.com> Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>