Code refactoring for end2end tests. 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>