[heap] Properly account for wasted bytes.

[heap] Properly account for wasted bytes.

- Wasted bytes are now accounted where they accrue, i.e., the corresponding free
  list. The amount of waste is transferred by concatenating free lists.
- During concatenation, free lists are no longer locked on FreeListCategory
  level, but in the FreeList itself, simplifying the sync between contained nodes
  and wasted bytes (which are effectively dropped nodes).

This is pre-work for properly moving memory to compaction spaces, which requires
correct accounting of wasted memory.

BUG=chromium:524425
LOG=N

Committed: https://crrev.com/7a6f47fe22323b574f2fffe5425a16ba516fd7a5
Cr-Commit-Position: refs/heads/master@{#31040}

[Michael Lippautz, 2015-09-30 15:01:58]

The CQ bit was checked by mlippautz@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-30 15:02:03]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1379833002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1379833002/1

[commit-bot: I haz the power, 2015-09-30 15:25:11]

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

[commit-bot: I haz the power, 2015-09-30 15:25:12]

Dry run: This issue passed the CQ dry run.

[Michael Lippautz, 2015-09-30 18:32:35]

The CQ bit was checked by mlippautz@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-09-30 18:32:54]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1379833002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1379833002/20001

[commit-bot: I haz the power, 2015-09-30 18:55:52]

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

[commit-bot: I haz the power, 2015-09-30 18:55:52]

Dry run: This issue passed the CQ dry run.

[Michael Lippautz, 2015-10-01 07:50:04]

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

[Michael Lippautz, 2015-10-01 07:50:05]

PTAL (also at ia32 perf)

[Hannes Payer (out of office), 2015-10-01 08:10:24]

lgtm

[Michael Lippautz, 2015-10-01 08:12:25]

The CQ bit was checked by mlippautz@chromium.org

[commit-bot: I haz the power, 2015-10-01 08:12:36]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1379833002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1379833002/20001

[commit-bot: I haz the power, 2015-10-01 08:14:14]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-01 08:14:33]

Patchset 2 (id:??) landed as
https://crrev.com/7a6f47fe22323b574f2fffe5425a16ba516fd7a5
Cr-Commit-Position: refs/heads/master@{#31040}