Move the EGL shared image creation implementation to the context. BUG=18110152 Change-Id: I21aece83756f033f579f11c0fb2e9e3d21f93703 Reviewed-on: https://swiftshader-review.googlesource.com/1262 Reviewed-by: Nicolas Capens <nicolascapens@google.com> Tested-by: Nicolas Capens <nicolascapens@google.com>