This should restore the old behavior of giving low priority to
newly-added live ranges.

Bug: chromium:859021
Change-Id: If22c9a1d0897d82623eb141fa03c30110e68bfc4
Reviewed-on: https://chromium-review.googlesource.com/1122402Reviewed-by: Stephan Herhut <herhut@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54142}