My recent change
https://chromium-review.googlesource.com/c/v8/v8/+/1570666 introduced an
error, found by ClusterFuzz, because I forgot to use EnsureSpace in a
new method in assembler-x64.

Bug: chromium:959014
Change-Id: I4c1b564b05de6d4403632e1521520f87706d56c9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1594977
Auto-Submit: Seth Brenith <seth.brenith@microsoft.com>
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61219}