Reland^2 "Filter invalid slots out from the SlotsBuffer after marking."

Reland^2 "Filter invalid slots out from the SlotsBuffer after marking."

And reland "Use a slot that is located on a heap page when removing
invalid entries from the SlotsBuffer."

This reverts commits de018fbda32e8ac57d8440e8fe6c3d3386bb9b11 and
d23a9f7a3e509bd405e1e4b0b851e463a4a736c2.

Reason for relanding: looking fine on Canary, let's get these fixes back in.

BUG=chromium:454297, chromium:470801
LOG=y
TBR=ishell@chromium.org

Committed: https://crrev.com/c24ed0a27798f13c9efb005c7e309c2fef21656a
Cr-Commit-Position: refs/heads/master@{#27507}

[Jakob Kummerow, 2015-03-28 17:41:53]

jkummerow@chromium.org changed reviewers:
+ ishell@chromium.org

[Jakob Kummerow, 2015-03-28 17:42:24]

The CQ bit was checked by jkummerow@chromium.org

[commit-bot: I haz the power, 2015-03-28 17:42:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1043703003/1

[commit-bot: I haz the power, 2015-03-28 18:04:09]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-03-28 18:04:28]

Patchset 1 (id:??) landed as
https://crrev.com/c24ed0a27798f13c9efb005c7e309c2fef21656a
Cr-Commit-Position: refs/heads/master@{#27507}