port e607e12e (r37323)

  original commit message:
  Introduce a new machine operator Float64Pow that for now is backed by
  the existing MathPowStub to start the unification of Math.pow, and at
  the same time address the main performance issue that TurboFan still has
  with the imaging-darkroom benchmark in Kraken.

  Also migrate the Math.pow builtin itself to a TurboFan builtin and
  remove a few hundred lines of hand-written platform code for special
  handling of the fullcodegen Math.pow version.

BUG=

Review-Url: https://codereview.chromium.org/2119773003
Cr-Commit-Position: refs/heads/master@{#37468}