Change the hydrogen timing data to include zone allocation.

Change the hydrogen timing data to include zone allocation.

Committed: http://code.google.com/p/v8/source/detail?r=6249

[Kevin Millikin (Chromium), 2011-01-10 14:03:40]

This adds a counter that's incremented on every zone allocation.

If you think that's too invasive, we could instead piggyback on growing a Zone
segment and provide an interface to set a watermark and read allocation since
the watermark.

[Mads Ager (chromium), 2011-01-10 14:13:59]

LGTM

Let's see if we can measure the overhead. I'd guess that it will not make much
of a difference.