Encapulate the ESSL compiler into a GL object that is per-context. * Allows for multiple contexts have to have different client versions, caps and extensions without causing shader compilation failures. BUG=angle:823 Change-Id: I523679e90be031b0b7fa385d46d6839b1cf3029f Reviewed-on: https://chromium-review.googlesource.com/227710 Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>