The previous logic had 2 if-elses, but the branch taken in the first one
determines the branch taken in the second one too (so there are 2 possibilities,
not 4). Make the structure reflect this.

BUG=v8:8015

Change-Id: I75ce86aa9731c0cae21c82f9aad6c83cb950e0d6
Reviewed-on: https://chromium-review.googlesource.com/1163613Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54947}