This change:
1) uses the new style ANGLE_SKIP_TEST_IF to skip tests.
2) replaces compile-time definition for OSX to skip tests by run-time
function IsOSX() to skip tests, in order to align with ANGLE_SKIP_TEST_IF.
3) fixes a couple of typos.

BUG=angleproject:2005

Change-Id: I5af77d82257536b9eb79e26afa502f5b91ff6d31
Reviewed-on: https://chromium-review.googlesource.com/915861
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>