Support CHROMIUM_path_rendering fragment operations This brings two new APIs, BindFragmentInputLocation and ProgramPathFragmentInputGen that together dictate how the fragment shader varyings are used. BUG=angleproject:1382 Change-Id: I4b52fd8a3555235a73aecd4f3dba2d500789cbb0 Reviewed-on: https://chromium-review.googlesource.com/357071 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Sami Väisänen <svaisanen@nvidia.com> Commit-Queue: Sami Väisänen <svaisanen@nvidia.com>