[NavigationTiming] Finalizing NavigationTiming

Hi, folks,

   Great works on the NavigationTiming! Kudos to everyone. It proves that we
don't need years to get something standardized. :-)

   There still seems to be a couple details missing from the current draft,
which I would like to get clarified before moving to CR.

1. SOP
   The current spec states that
    * redirectStart/End are available only if *all* the redirects are from
the same origin.
    * unloadEventStart/End are available if previous document and the
current document are from the same origin
   So in the following case:
    *<previous page on a.com>* -------click----> *<a.com>* ------redirect---->
*<b.com>* ------redirect-----> *<a.com>*
     redirectStart/End are not available, but unloadEventStart/End are
available. Is this what we want? This still fits our security/privacy
discussion but I would like to point it out explicitly.

2. We should add that navigationStart will not be available if there is
cross-origin redirects. I believe this is our decision but it is missing
from the definition. (On the other hand, navigationStart will be always
available if there is no redirection.)

3. It should be added that domainLookupStart/End must return the same value
as fetchStart in case persistent connection is used.

   If these look fine, I will update the draft shortly.

cheers,
Zhiheng