requestStart and fetchStart

    In the last conf call, we decided to have requestStart always include
the cache lookup time.
It takes care of Sigbjørn's
feedback<http://lists.w3.org/Archives/Public/public-web-perf/2010Sep/0017.html>
about
requestStart inconsistency and fit the implementation
constrains in some user agents. Here is a follow-up and RFC.

    The current navigation
model<http://dev.w3.org/html5/spec/Overview.html#navigate> in
HTML5 places the cache lookup right before the fetching
process<http://dev.w3.org/html5/spec/Overview.html#fetch>
.
So strictly speaking, requestStart comes after fetchStart, even though the
difference should be minor.
And, in case of a cache hit, domainLookupStart/End and connectStart/End
should take requestStart's
value instead of fetchStart's as it is right now.

   This is my preference but I believe it is different from the current
implementation found in IE-beta
and Chrome. So comments are welcome.

cheers,
Zhiheng