Our current deserializers (startup & partial) use a system of static memory
reservations: required memory is determined at serialization time, which we
then request before deserialization and dole out as-needed during
deserialization.

Lazy builtin deserialization needs a bit more flexibility. On the one hand, the
amount of required memory varies since --lazy-deserialization can be switched
on and off at runtime.

On the other, builtin deserialization has been made order-independent, and we
can encounter references to builtins before they have been deserialized.

Both problems are solved by dynamically allocating required memory and
initializing the builtins table with the (yet uninitialized) builtin Code
objects.

Bug: v8:6624
Change-Id: Iee90992e91adb4ab45dae1acc81f64a108d12584
Reviewed-on: https://chromium-review.googlesource.com/647748
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47789}