[heap] No leakage of incremental-marking.h outside of heap.

[heap] No leakage of incremental-marking.h outside of heap.

This prevents the internal incremental-marking.h to be usable outisde
of the "heap" directory. The logic inside that component is only useful
within the GC and is now properly encapsulated.

R=hpayer@chromium.org

Committed: https://crrev.com/ddafe2c4940ae20a7c925047d27b54be234cada4
Cr-Commit-Position: refs/heads/master@{#31010}

[Hannes Payer (out of office), 2015-09-29 16:56:38]

lgtm

[Hannes Payer (out of office), 2015-09-29 16:56:42]

The CQ bit was checked by hpayer@chromium.org

[commit-bot: I haz the power, 2015-09-29 16:56:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1374203002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1374203002/1

[commit-bot: I haz the power, 2015-09-29 16:59:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-09-29 16:59:27]

Patchset 1 (id:??) landed as
https://crrev.com/ddafe2c4940ae20a7c925047d27b54be234cada4
Cr-Commit-Position: refs/heads/master@{#31010}