Passing floating point params to/from C has never quite worked correctly,
but we've never enforced the restriction early in the CallDescriptor
creation process because of unittests. Fix unittests to make their own
simple call descriptors and not rely on the C ones.

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1701593003

Cr-Commit-Position: refs/heads/master@{#33993}