We use JSCreateClosure to also constructs closures for builtins, i.e.
for the callbacks created by the Promise constructor. For these builtins
we cannot set code to CompileLazy builtin, but need to use the code from
the SharedFunctionInfo. The explicit mode tells the lowering what it
should do (instead of relying on SharedFunctionInfo::native(), which is
not the right bit).

Bug: v8:2206, v8:7253, v8:7310
Change-Id: Ic956814e137c57b36ebb5d7b4d964dde5ee51a0d
Reviewed-on: https://chromium-review.googlesource.com/930964
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51547}