We only want to record resource timing for the load that was initiated
by parent document. We filter out subsequent navigations for <iframe>,
but we should do it for other types of subframes too.

Bug: 780312
Change-Id: I3a7b9e1a365c99e24bb8dac190e88c7099fc3da5
Reviewed-on: https://chromium-review.googlesource.com/750487
Reviewed-by: Nate Chapin <[email protected]>
Commit-Queue: Kunihiko Sakamoto <[email protected]>
Cr-Commit-Position: refs/heads/master@{#513665}