[heap] Separate ObjectStats out into its own class.

[heap] Separate ObjectStats out into its own class.

Note that this is only pulling out the bookkeeping side of things, the
marking visitor that actually records the statistics should also move
into the ObjectStats class. That will be done as a follow-up.

R=mlippautz@chromium.org

Committed: https://crrev.com/c7de3e7f27fb4068191a6434f47d20191e676ed6
Cr-Commit-Position: refs/heads/master@{#30547}

[Michael Lippautz, 2015-09-02 16:32:46]

lgtm

[Michael Starzinger, 2015-09-02 16:41:53]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-09-02 16:42:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1326793002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1326793002/1

[commit-bot: I haz the power, 2015-09-02 16:43:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-02 16:43:51]

Patchset 1 (id:??) landed as
https://crrev.com/c7de3e7f27fb4068191a6434f47d20191e676ed6
Cr-Commit-Position: refs/heads/master@{#30547}