Port 30fabc4c

Original Commit Message:

    This ensures that there is only one entrance point from C++ to
    generated code, hence only one method has to be excluded from CFI.
    It also introduces type safety by only allowing the code to be called
    with the right arguments.
    This CL includes minor drive-by fixes in the tests, like removing
    unused dummy variables.

R=clemensh@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: Idb21a7b8103a8fb833c963c182463006d9dd6288
Reviewed-on: https://chromium-review.googlesource.com/857425Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#50490}