Add a makeCurrent method to Display. BUG=angle:658 Change-Id: If1830fb164d31e2ee8092414d012e127ec344d69 Reviewed-on: https://chromium-review.googlesource.com/242033 Reviewed-by: Kenneth Russell <kbr@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Tested-by: Geoff Lang <geofflang@chromium.org>