Remove V8.ZoneSegmentBytes.

Remove V8.ZoneSegmentBytes.

1) It's unused. 2) Since Zones can be used on a background thread, the Zone
cannot just access this counter from the Isolate, so keeping this counter up to
date would require extra work. Better to just remove it.

BUG=431860
LOG=n
R=yangguo@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=25263

[marja, 2014-11-11 13:30:33]

marja@chromium.org changed reviewers:
+ yangguo@chromium.org

[marja, 2014-11-11 13:30:34]

yangguo, ptal

[Yang, 2014-11-11 13:34:16]

On 2014/11/11 13:30:34, marja wrote:
> yangguo, ptal

lgtm.

[marja, 2014-11-11 14:26:12]

Routing some offline (really offline) discussion.

1) So afawk, on the Chrome side counters should be thread safe. Though, there's
no way to access the data produced by the background threads, so it's useless.
2) On the V8 side, the Counters class is not thread safe
3) Thus, background threads shouldn't muck with it (that is, the state after
this CL is more correct than before)
4) Counters contains other stuff like histogram timers which are definitely not
thread safe.
5) The real fix to my problem (see bug) is on the Blink side anyway, so this CL
is not super important.

This CL is by no means a long term solution and not strictly needed, but the
state of the world is still better after it than before.

[marja, 2014-11-11 14:27:33]

Committed patchset #1 (id:1) manually as 25263 (presubmit successful).