shiny/driver/internal/lifecycler: add a drawContext arg.

The X11 gldriver doesn't set this, but it should, to be consistent with
Mac and Windows.

Change-Id: If64a65ba2efde9ecc90a5d1b0289441f6724005f
Reviewed-on: https://go-review.googlesource.com/25322
Reviewed-by: David Crawshaw <crawshaw@golang.org>
5 files changed