[heap] Separate scavenger functionality into own file.

[heap] Separate scavenger functionality into own file.

This moves scavenging functionality into a separate component so that
neither the scavenger nor objects-visiting need to be exposed outside
the heap.

R=hpayer@chromium.org,mlippautz@chromium.org

Committed: https://crrev.com/ea25bf05f8fd61f99c928baad63c8101415e8788
Cr-Commit-Position: refs/heads/master@{#30712}

[Michael Starzinger, 2015-09-04 09:31:09]

mstarzinger@chromium.org changed reviewers:
+ hpayer@chromium.org, mlippautz@chromium.org

[Michael Lippautz, 2015-09-04 13:45:07]

Benchmark results seem to be fine, i.e., all numbers within noise.

I don't see why wee would need to embbed the scavenger (caching?), so I am fine
with this change. Let's wait for Hannes on this one too though.

[Michael Starzinger, 2015-09-04 15:00:41]

Thanks. Yes, I definitely want to get Hannes' opinion on this too.

[Hannes Payer (out of office), 2015-09-14 10:34:32]

LGTM, no performance impact.

[Michael Starzinger, 2015-09-14 10:52:31]

The CQ bit was checked by mstarzinger@chromium.org

[Michael Starzinger, 2015-09-14 10:52:31]

The patchset sent to the CQ was uploaded after l-g-t-m from hpayer@chromium.org
Link to the patchset: https://codereview.chromium.org/1323993004/#ps80001
(title: "Rebased.")

[commit-bot: I haz the power, 2015-09-14 10:52:41]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1323993004/80001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1323993004/80001

[commit-bot: I haz the power, 2015-09-14 11:44:27]

Committed patchset #5 (id:80001)

[commit-bot: I haz the power, 2015-09-14 11:44:42]

Patchset 5 (id:??) landed as
https://crrev.com/ea25bf05f8fd61f99c928baad63c8101415e8788
Cr-Commit-Position: refs/heads/master@{#30712}