port ec132e05 (r40086)

  original commit message:
  (GcStress failure was unrelated.)

  At one time, we hoped to generate the same code for different
  native contexts. But in truth, much performance comes from optimizing
  on the native context. Now we abandon this pathway.

BUG=

Review-Url: https://codereview.chromium.org/2404843002
Cr-Commit-Position: refs/heads/master@{#40147}