All OpenGL functions are now methods on a Context interface. The
gl.Context matches the one loaded into thread-local storage in C.
For mobile apps, the context is owned by an app.App. For now, it is
provided through the events channel on a lifecycle event. Long-term,
it should probably be available by a method on app.App, but this is
inherently racey with our current use of a channel to deliver events.
Shiny-based programs will have a gl.Context associated with a each
shiny.Window. The expectation is each Window will have different
contexts, allowing them to draw separately.
Change-Id: Ie09986fb74e493129f2ea542a151c95c6fa29812
Reviewed-on: https://go-review.googlesource.com/13431
Reviewed-by: Nigel Tao <nigeltao@golang.org>
