scheduler: Encapsulate task queue selector inside the scheduler helper

scheduler: Encapsulate task queue selector inside the scheduler helper

Encapsulate task queue selector inside the scheduler helper to avoid
clients changing task queue states in an uncontrolled way.
This will be needed by the upcoming shutdown task queue.

No functional changes.

BUG=463143
Committed: https://crrev.com/a08639cd15b52dfb784cc94295e9fc13823b1d71
Cr-Commit-Position: refs/heads/master@{#326833}

[Sami, 2015-04-24 17:02:43]

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

[rmcilroy, 2015-04-24 17:05:30]

On 2015/04/24 17:02:49, Sami wrote:

lgtm, thanks!

[Sami, 2015-04-24 17:09:31]

The CQ bit was checked by skyostil@chromium.org

[Sami, 2015-04-24 17:09:43]

The CQ bit was unchecked by skyostil@chromium.org

[Sami, 2015-04-24 17:10:00]

The CQ bit was checked by skyostil@chromium.org

[commit-bot: I haz the power, 2015-04-24 17:10:31]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1103853004/1

[commit-bot: I haz the power, 2015-04-24 17:59:38]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-24 18:00:20]

Patchset 1 (id:??) landed as
https://crrev.com/a08639cd15b52dfb784cc94295e9fc13823b1d71
Cr-Commit-Position: refs/heads/master@{#326833}