Re-use callback objects in the DataUseAggregator.

Re-use callback objects in the DataUseAggregator.

This CL makes the DataUseAggregator re-use the same callback objects
separately for annotation and amortization calls, as an optimization to
avoid allocating and holding on to a new callback object for every call.
This CL should have no noticible effects other than using less memory.

BUG=

Committed: https://crrev.com/2955091ca0b685a7a08a335df14f70c7eceeb0bc
Cr-Commit-Position: refs/heads/master@{#360437}

[sclittle, 2015-11-18 00:14:42]

sclittle@chromium.org changed reviewers:
+ tbansal@chromium.org

[tbansal1, 2015-11-18 00:54:40]

lgtm

[sclittle, 2015-11-18 01:09:52]

The CQ bit was checked by sclittle@chromium.org

[commit-bot: I haz the power, 2015-11-18 01:11:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1456793003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1456793003/1

[commit-bot: I haz the power, 2015-11-18 01:51:28]

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

[commit-bot: I haz the power, 2015-11-18 01:51:29]

Try jobs failed on following builders:
  linux_chromium_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)
  win_chromium_x64_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[sclittle, 2015-11-18 02:30:32]

The CQ bit was checked by sclittle@chromium.org

[sclittle, 2015-11-18 02:30:32]

The patchset sent to the CQ was uploaded after l-g-t-m from tbansal@chromium.org
Link to the patchset: https://codereview.chromium.org/1456793003/#ps20001
(title: "Rebased on master")

[commit-bot: I haz the power, 2015-11-18 02:30:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1456793003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1456793003/20001

[commit-bot: I haz the power, 2015-11-18 02:50:27]

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

[commit-bot: I haz the power, 2015-11-18 02:50:28]

Try jobs failed on following builders:
  linux_chromium_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[sclittle, 2015-11-18 21:55:31]

The CQ bit was checked by sclittle@chromium.org

[sclittle, 2015-11-18 21:55:31]

The patchset sent to the CQ was uploaded after l-g-t-m from tbansal@chromium.org
Link to the patchset: https://codereview.chromium.org/1456793003/#ps40001
(title: "Fixed WeakPtr threading issue.")

[commit-bot: I haz the power, 2015-11-18 21:55:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1456793003/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1456793003/40001

[commit-bot: I haz the power, 2015-11-18 23:09:16]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-11-18 23:10:10]

Patchset 3 (id:??) landed as
https://crrev.com/2955091ca0b685a7a08a335df14f70c7eceeb0bc
Cr-Commit-Position: refs/heads/master@{#360437}