port d1b3d426 (r35918)

  original commit message:
  Further refactor the pipeline to even run the first scheduler (part of
  the effect control linearization) concurrently. This temporarily
  disables most of the write barrier elimination, but we will get back to
  that later.

  Drive-by-fix: Remove the dead code from ChangeLowering, and stack
  allocate the Typer in the pipeline. Also migrate the AllocateStub to a
  native code builtin, so that we have the code object + a handle to it
  available all the time.

BUG=

Review-Url: https://codereview.chromium.org/1940143002
Cr-Commit-Position: refs/heads/master@{#35961}