- simplify prototype traversal.
- use V8InspectorClient::isInspectableHeapObject since some embedders
  on JavaScript heap contains not inspectable objects, e.g. wrapper
  boilerplates in blink.
- Runtime.queryObjects takes prototype object as argument for more
  flexibility.

R=alph@chromium.org

Bug: v8:6732
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I06f0d5c987150c80c3e9b05e7f6ad195985fc539
Reviewed-on: https://chromium-review.googlesource.com/627577
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47559}