Inherit referrer and policy when creating a nested browsing context

BUG=763194
R=estark@chromium.org

Change-Id: Ide3950269adf26ba221f573dfa088e95291ab676
Reviewed-on: https://chromium-review.googlesource.com/732652
Reviewed-by: Emily Stark <estark@chromium.org>
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511211}
  explicit NetworkStateObserver(Document& document)
      : ContextLifecycleObserver(&document) {
    online_observer_handle_ = GetNetworkStateNotifier().AddOnLineObserver(
        this,
        TaskRunnerHelper::Get(TaskType::kNetworking, GetExecutionContext()));
  }

  explicit NetworkStateObserver(Document& document)
      : ContextLifecycleObserver(&document) {
    online_observer_handle_ = GetNetworkStateNotifier().AddOnLineObserver(
        this,
        TaskRunnerHelper::Get(TaskType::kNetworking, GetExecutionContext()));
  }
