This will allow for passing more than one variable. This is
particularly interesting for calling a method on each type in a
parameter pack, as in:

template<typename... T>
void foo(T&&... ts) {
  USE(do_something(ts)...);
}

Drive-by fix: Allow to pass arbitrary types to USE, including
references. This might prevent a copy for pass-by-value.

R=ishell@chromium.org

Change-Id: I8f894d730bbcd195ed83705f98771994b4bc906f
Reviewed-on: https://chromium-review.googlesource.com/565561Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46527}