Plumb robust resource init extensions. This also cleans up a few minor glitches in the extension texts, and renames the EGL extension for consistency. It incidentally fixes a bug in our EGL init where we were checking the wrong client versions for KHR_create_context. It also implements a new feature for tests which allow them to defer Context creation until the test body. This allows tests to check for EGL extension available before trying to create a context with certain extensions. BUG=angleproject:1635 Change-Id: I9311991332c357e36214082b16f2a4a57bfa8865 Reviewed-on: https://chromium-review.googlesource.com/450920 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>