Added field to error structures to signal existence of a stale copy in
the cache, for use by the navigation source.

BUG=329620

Review URL: https://codereview.chromium.org/138493002

git-svn-id: svn://svn.chromium.org/blink/trunk@165973 bbb929c8-8fbe-4397-9dbb-9b2b20218538