150 is too high for some people.

Reports of 132, 145, 149 on OS X.

Fixes #18203

Change-Id: I559639aba7e87e07d1a1249f8b212b3f34a078ab
Reviewed-on: https://go-review.googlesource.com/34019Reviewed-by: Russ Cox <rsc@golang.org>