Even though we were generating additional arguments with default value
in the case that the caller was not providing enough, we then passed
the original pointer, leading to potential out-of-bounds accesses.

R=ahaas@chromium.org

Bug: chromium:763294,chromium:763297
Change-Id: Id18622d0d40e0408e26a5fc6f97494b5f9e18d17
Reviewed-on: https://chromium-review.googlesource.com/657699Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47930}