Proxy's call trap can be used to cause recursion.

R=bmeurer@chromium.org, tebbi@chromium.org

Bug: chromium:779344
Change-Id: I19c989f618f7230028ebe18c3415bc3f4bd72b93
Reviewed-on: https://chromium-review.googlesource.com/743782Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49069}