Prior to a refactoring of sessions_sync_manager, page_urls were
implicitly filtered for validity by only using those that matched the
url of a local tab. With this filtering gone, there are scenarios that
can result in invalid urls being sent. Rather than trying to figure out
all these scenarios, it seems safer to just not forward these urls at
all.

R=zea@chromium.org
BUG=769008

Change-Id: I5068842577b4625c21057d5a022145ebf3415948
Reviewed-on: https://chromium-review.googlesource.com/752541


Reviewed-by: Nicolas Zea <zea@chromium.org>
Commit-Queue: Patrick Noland <pnoland@google.com>
Cr-Commit-Position: refs/heads/master@{#513630}