Simplify the creation of OS-specific windows and timers in the samples. BUG=angle:521 Change-Id: I9550269e9cd67fc24246853bec3c1f67cb16da2a Reviewed-on: https://chromium-review.googlesource.com/211130 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shannon Woods <shannonwoods@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>