Validate in-process plugin instance messages.

Bug: 733548, 733549
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_site_isolation
Change-Id: Ie5572c7bcafa05399b09c44425ddd5ce9b9e4cba
Reviewed-on: https://chromium-review.googlesource.com/538908
Commit-Queue: Bill Budge <bbudge@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#480696}
const base::Process& BrowserPpapiHostImpl::GetPluginProcess() const {
  DCHECK(in_process_ || plugin_process_.IsValid());
  return plugin_process_;
}

const base::Process& BrowserPpapiHostImpl::GetPluginProcess() const {
  DCHECK(in_process_ || plugin_process_.IsValid());
  return plugin_process_;
}
