Permit trailing comma after call arguments.
Permit trailing comma after call arguments.

R=iant
https://golang.org/cl/1674043

anlhord/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,qskycolor/gofrontend,golang/gofrontend,qskycolor/gofrontend,anlhord/gofrontend,anlhord/gofrontend,golang/gofrontend,qskycolor/gofrontend,golang/gofrontend,qskycolor/gofrontend,qskycolor/gofrontend