cc: Use std::map instead of hash_map for TaskGraphRunner namespaces.

cc: Use std::map instead of hash_map for TaskGraphRunner namespaces.

This avoids some heap allocations and provides more than good enough
namespace lookup performance for the number of namespaces used in
practice. Also provides a ~300% performance improvement in cases
where the task graph only contains a single task.

BUG=246546
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=250222

[vmpstr, 2014-02-10 16:52:51]

lgtm. What do you mean 300% improvement with a single task? Do you mean a single
task namespace? I don't see how changing the namespace map would affect single
task performance, unless I'm missing something

[reveman, 2014-02-10 17:26:40]

On 2014/02/10 16:52:51, vmpstr wrote:
> lgtm. What do you mean 300% improvement with a single task? Do you mean a
single
> task namespace? I don't see how changing the namespace map would affect single
> task performance, unless I'm missing something

Performance when scheduling a single task is actually improved by this much.
Thanks to previous changes, SetTaskGraph performance is now at a level where
doing one lookup+erase+insert in a hash map per call is enough to slow us down
by this much. It wouldn't have been noticeable in the past as other parts of
SetTaskGraph were too slow..

[reveman, 2014-02-10 17:26:47]

The CQ bit was checked by reveman@chromium.org

[commit-bot: I haz the power, 2014-02-10 17:26:53]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/reveman@chromium.org/131543014/1

[commit-bot: I haz the power, 2014-02-10 18:23:18]

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

[commit-bot: I haz the power, 2014-02-10 18:23:20]

Retried try job too often on win_rel for step(s) unit_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

[reveman, 2014-02-10 18:44:31]

The CQ bit was checked by reveman@chromium.org

[commit-bot: I haz the power, 2014-02-10 18:44:42]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/reveman@chromium.org/131543014/1

[commit-bot: I haz the power, 2014-02-10 22:29:58]

Change committed as 250222