In the case of a corrupted snapshot we fall back to initializing the isolate
from scratch. Howver, we don't ship the full SetupIsolateDelegate. This causes
spurious failures during later initialization.

This CL mostly turns the DCHECKs in SetupIsolateDelegate into hard CHECKs making
it easier to spot these kind of failures.


Bug: chromium:767846
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Ibe8a5beece27433439b1b09412f6110be703ff86
Reviewed-on: https://chromium-review.googlesource.com/779189Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49533}