The OpenGL backend can't gather discover default adapters because it
needs getProc to do anything so we add DiscoverAdapters method to
Instance that takes backend-specific options.
dawn_native::opengl::CreateDevice is removed in favor of the adapter
path so OpenGLBinding is modified to create an instance locally. This is
only temporary until all backends support adapters, at which point a lot
of *Binding code will be factored.
Also contains a small fix for Result<T, E> with movable types.
BUG=dawn:29
Change-Id: I4eb3d4a14a871af73e1872132aff72b45e5fe566
Reviewed-on: https://dawn-review.googlesource.com/c/3663
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
