Otherwise we might reuse a node that is scheduled later in the unchanged block.

BUG=v8:9684

Change-Id: I655b538384d5ed8782d3d9bbb883037462003693
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1881155
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64594}