Perf-sheriffs please revert if this causes any performance regressions.

BUG=

Change-Id: I9ead7148e1e0146ece3614df49fd031dd1e357fe
Reviewed-on: https://chromium-review.googlesource.com/445159
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44143}