Because in the C++ API, a Proxy is an Object

BUG=none
R=bmeurer@chromium.org
LOG=n
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng

Review URL: https://codereview.chromium.org/1590873003

Cr-Commit-Position: refs/heads/master@{#33329}