Extend multiview perf tests to cover all extension code paths The ANGLE_multiview extension can be supported with three possible code paths - through view being selected in the vertex shader on D3D and OpenGL, and through the view being selected in the geometry shader on D3D only. This patch extends the multi-view performance tests to benchmark these three different code paths. BUG=angleproject:2062 TEST=angle_end2end_tests Change-Id: I443e4db64a95eede1142718a43a095ee5a03738c Reviewed-on: https://chromium-review.googlesource.com/652466 Commit-Queue: Martin Radev <mradev@nvidia.com> Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>