Make the onDestroy method generic to use different context and error types.

This will allow us to have RefCountObjects for EGL that return EGL errors
and destroy with egl::Displays.

BUG=angleproject:2668

Change-Id: I77549cdc7119979d6eec96c7e6246242aed74830
Reviewed-on: https://chromium-review.googlesource.com/1153452
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>