[heap] Remove obsolete Heap::sweep_generation field.

[heap] Remove obsolete Heap::sweep_generation field.

R=mlippautz@chromium.org

Committed: https://crrev.com/373c0b511aa065493b41a5f5dcb289f613cdfc45
Cr-Commit-Position: refs/heads/master@{#30253}

[Michael Lippautz, 2015-08-19 14:21:09]

lgtm % compilation errors

[Michael Starzinger, 2015-08-19 15:19:33]

The CQ bit was checked by mstarzinger@chromium.org

[Michael Starzinger, 2015-08-19 15:19:33]

The patchset sent to the CQ was uploaded after l-g-t-m from
mlippautz@chromium.org
Link to the patchset: https://codereview.chromium.org/1289963006/#ps20001
(title: "Fix Windows compilation.")

[commit-bot: I haz the power, 2015-08-19 15:19:46]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-19 15:19:47]

This CL has an open dependency (Issue 1285183010 Patch 20001). Please resolve
the dependency and try again.

[Michael Starzinger, 2015-08-19 15:21:26]

Well, thank you CQ, but no thank you.

[Michael Starzinger, 2015-08-19 15:21:30]

The CQ bit was checked by mstarzinger@chromium.org

[Michael Starzinger, 2015-08-19 15:21:30]

The patchset sent to the CQ was uploaded after l-g-t-m from
mlippautz@chromium.org
Link to the patchset: https://codereview.chromium.org/1289963006/#ps40001
(title: "Drop bogus dependency.")

[commit-bot: I haz the power, 2015-08-19 15:21:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1289963006/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1289963006/40001

[commit-bot: I haz the power, 2015-08-19 16:09:47]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-08-19 16:10:07]

Patchset 3 (id:??) landed as
https://crrev.com/373c0b511aa065493b41a5f5dcb289f613cdfc45
Cr-Commit-Position: refs/heads/master@{#30253}