Add UBO offset support for D3D11.1. Also fixes the uniform count upper limit in glGetActiveUniformsiv, as well as an assert hit with used but unbound uniform buffer. BUG=angleproject:507 BUG=angleproject:962 Change-Id: I096fe1c9b4f0f398f3a638cd8311278987dfb7dc Reviewed-on: https://chromium-review.googlesource.com/263404 Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Gregoire Payen de La Garanderie <Gregory.Payen@imgtec.com>