We currently report description field for numbers. On client side user
can calculate description as remoteObject.unserializableValue ||
(remoteObject.value + ''). Let's report description only for objects to
simplify value -> remoteObject logic a bit.

R=dgozman@chromium.org
TBR=jgruber@chromium.org

Bug: chromium:595206
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I91356a44aa3024e20c8f966869abf4a41b88e4bc
Reviewed-on: https://chromium-review.googlesource.com/737485
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Pavel Feldman <pfeldman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53453}