When encountering a JSFunction, generate its initial map (if
appropriate).  This ensures that we can depend on the initial
map during optimization.

We are not sure about the performance impact of this change, it
might cause regressions.

R=jarin@chromium.org, mslekova@chromium.org

Bug: v8:7790, chromium:875175
Change-Id: I4bbf62e30730f55a53d9bb7eee62c87d820616fb
Reviewed-on: https://chromium-review.googlesource.com/1180970Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55253}