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}
scoped_refptr<WebTaskRunner> Document::GetTaskRunner(TaskType type) {
  if (ContextDocument() && ContextDocument()->GetFrame())
    return ContextDocument()->GetFrame()->FrameScheduler()->GetTaskRunner(type);
  return Platform::Current()->CurrentThread()->GetWebTaskRunner();
}

scoped_refptr<WebTaskRunner> Document::GetTaskRunner(TaskType type) {
  if (ContextDocument() && ContextDocument()->GetFrame())
    return ContextDocument()->GetFrame()->FrameScheduler()->GetTaskRunner(type);
  return Platform::Current()->CurrentThread()->GetWebTaskRunner();
}
