No usage sites are getting the length for uncompiled functions, so we can
postpone setting the correct length until after compilation. This way we don't
need to produce and store it for skipped inner functions.

In the current implementation, getting the function length compiles it (and
users rely on it - so the feature is probably not going to go away).

BUG=v8:5516

Change-Id: Id8c9a05d2391505a6cde613841094170c9a1b808
Reviewed-on: https://chromium-review.googlesource.com/468927
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Daniel Vogelheim <vogelheim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44679}