About window.performance namespace

Hi, folks,

   In today's conf call, the group discussed the issue of using
window.performance namespace. The following proposal was
brought up in a follow-up meeting this afternoon. It has been acknowledged
by Anderson/Nic (IE) and Tony/James (Chrome)
and we would like to hear feedback from others as well.

   Proposal:
     * NavigationTiming will use window.performance namespace.
     * window.performance will be replaceable
     * window.performance.timing and window.performance.navigation will be
kept read-only.

   Having window.performance replaceable avoid breaking existing
javascripts. Keeping the timing and navigation objects read-only
does not guarantee the integrity of timing attributes but makes forging
these interfaces less trivial.

   Please share your thoughts.

cheers,
Zhiheng