Apply stack churn/size tweaks to Prog::IsOnePass().
Apply stack churn/size tweaks to Prog::IsOnePass().

Change-Id: I46f449bb6564888aa1eb386bbb9171354c038d06
Reviewed-on: https://code-review.googlesource.com/4841
Reviewed-by: Paul Wankadia <62d4e38bb1380f055ec4b899baa75e52af09c5f7@google.com>

google/re2,google/re2,google/re2,google/re2,google/re2