--cache=code produces and consume cache in different isolates. Earlier
we created a new isolate for the run consuming the code cache. This cl
changes to create a new isolate when producing the code cache so that
RunShell works as expected.

Change-Id: I1c73aab2bee429aafdcc52a68ddcf742edfcd652
Reviewed-on: https://chromium-review.googlesource.com/997694
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52424}