A couple of formats that required two extensions would OR the checks
together when they should have ANDed them and allowed the validation to be
too permissive.

Fixed the checks and added a new one that needs to OR the extension checks
together to verify GL_DEPTH24_STENCIL8_OES support.

BUG=angle:752

Change-Id: I2e1e12fd428358e975cd22eb685b9a8fb797161f
Reviewed-on: https://chromium-review.googlesource.com/219094Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>