Graph creation used to handle exception throwing gracefully, but this
seems to never happen, so turned it into a CHECK instead.

Change-Id: I90f8471fe77eb66402fd8abe0d5b15dcffee49bf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1784286
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63552}