Check that RWHI isn't deleted manually while owned by a scoped_ptr in RVHI

BUG=590284

Review URL: https://codereview.chromium.org/1747183002

Cr-Commit-Position: refs/heads/master@{#378844}
RenderWidgetHostImpl::GetAllRenderWidgetHosts() {
  scoped_ptr<RenderWidgetHostIteratorImpl> hosts(
      new RenderWidgetHostIteratorImpl());
  for (auto& it : g_routing_id_widget_map.Get())
    hosts->Add(it.second);

  return std::move(hosts);
}

RenderWidgetHostImpl::GetAllRenderWidgetHosts() {
  scoped_ptr<RenderWidgetHostIteratorImpl> hosts(
      new RenderWidgetHostIteratorImpl());
  for (auto& it : g_routing_id_widget_map.Get())
    hosts->Add(it.second);

  return std::move(hosts);
}
