Removes the overhead of Zone allocating temporary space
that only slightly improved performance of the overlap
(less common) case.

Bug: chromium:808360
Change-Id: Ic92f20f15decb12b916ee23267debd9adc785ee0
Reviewed-on: https://chromium-review.googlesource.com/904462Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Peter Wong <peter.wm.wong@gmail.com>
Cr-Commit-Position: refs/heads/master@{#51119}