[heap] Move IdentityMap data structure out of heap.

[heap] Move IdentityMap data structure out of heap.

This data structure uses the public heap API only and is not specific
to any heap internals. It should be usable throughout V8 and inclusion
of the header file should not be restricted.

R=titzer@chromium.org

Committed: https://crrev.com/3d7a34b5c744065a4e786645fe834ce30725c5fb
Cr-Commit-Position: refs/heads/master@{#30443}

[Michael Starzinger, 2015-08-28 11:54:46]

mstarzinger@chromium.org changed reviewers:
+ rmcilroy@chromium.org

[Michael Starzinger, 2015-08-28 11:54:47]

Ben: PTAL.
Ross: FYI.

[titzer, 2015-08-28 12:04:01]

On 2015/08/28 11:54:47, Michael Starzinger wrote:
> Ben: PTAL.
> Ross: FYI.

LGTM

[Michael Starzinger, 2015-08-28 12:05:04]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-08-28 12:05:14]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1320503004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1320503004/1

[commit-bot: I haz the power, 2015-08-28 13:01:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-28 13:01:18]

Patchset 1 (id:??) landed as
https://crrev.com/3d7a34b5c744065a4e786645fe834ce30725c5fb
Cr-Commit-Position: refs/heads/master@{#30443}

[rmcilroy, 2015-08-28 13:11:03]

lgtm, thanks!