This adds support for lazy deserialization of JS-linkage (TFJ) builtins,
still gated behind the --lazy-deserialization flag. If enabled, we
proceed as follows:

During isolate initialization, only eager builtins are deserialized. All
references to lazy builtins are replaced by the DeserializeLazy builtin.
In particular, this happens in the builtin table (Builtins::builtins_)
and in SharedFunctionInfo objects.

When calling into a not-yet deserialized function (i.e. the JSFunction's
code object is the DeserializeLazy builtin), the DeserializeLazy builtin
takes over.  It checks the builtin table to see if the target builtin
(determined by looking at the builtin id stored on the
SharedFunctionInfo) has already been deserialized. If so, it simply
copies the builtin code object to the JSFunction and SharedFunctionInfo.
Otherwise, we enter Runtime::kDeserializeLazy to deserialize the
builtin.

With --lazy-deserialization, isolate deserialization is 11% faster
(1.5ms vs.  1.7ms), and code_space->Size() is 33% lower (984K vs.
1475K).

Moving relocation infos & handler tables out of the partial snapshot
cache would additionally let us save up to 30K per isolate. Adding code
stubs to that list increases further potential savings to 262K.

Bug: v8:6624
Change-Id: I0ac7d05d165d2466998269bd431ac076a311cbeb
Reviewed-on: https://chromium-review.googlesource.com/649166
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47818}