This refactoring hides the fact that some wrappers are first generated
in the GC'ed heap and then copied into the native module. It is a first
step towards avoiding the redundant copy.

R=clemensh@chromium.org

Change-Id: I531fa42e8b4c210948d306624007348a39b981e0
Reviewed-on: https://chromium-review.googlesource.com/c/1333673
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57477}