Port a86384f1

Original commit message:
Also introduce new interface descriptors for the trampoline and full
versions of those stubs.

Currently, the stubs aren't functional.

R=mvstanton@chromium.org, dstence@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1159483003

Cr-Commit-Position: refs/heads/master@{#28636}