(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=
TBR=bmeurer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true

Review URL: https://codereview.chromium.org/2402663002 .

Cr-Commit-Position: refs/heads/master@{#40086}