Persist offline page info in a navigation entry if needed

The offline page info from extra request headers needs to be persisted
in serialized navigation entry in order for it to be restored when
Chrome restarts. Otherwise, we may be opening an online page without
this info.

The design doc for this can be found here: https://docs.google.com/document/d/1vz0a9N-9egdm3yMDYMHcNVmQHOL8Qglz54lgG4ATwhc

BUG=644553
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2310363002
Cr-Commit-Position: refs/heads/master@{#422542}
19 files changed