[bfcache] Don't cache documents when subframes are still loading.

By requiring all subframes to have loaded, we don't have to worry about
race conditions where a subframe was navigating at the time the document
was put into the cache.

Change-Id: Iecc4b4db8ccc961b70e9440053ee1a6b9352beba
Bug: 986742
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1741671
Commit-Queue: Lowell Manners <[email protected]>
Reviewed-by: Arthur Sonzogni <[email protected]>
Cr-Commit-Position: refs/heads/master@{#688992}
6 files changed