Move kDataReductionProxy registration to the data_reduction_proxy component.

Move kDataReductionProxy registration to the data_reduction_proxy component.

The pref data_reduction_proxy::prefs::kDataReductionProxy should have
been part of data_reduction_proxy::RegisterPrefs() to avoid having
all embedder register it manually just before call said function.

BUG=557814
Committed: https://crrev.com/00e1e6c710ed420e00cf457b5048d813b7a3c2cb
Cr-Commit-Position: refs/heads/master@{#361358}

[sdefresne, 2015-11-21 08:55:59]

sdefresne@chromium.org changed reviewers:
+ droger@chromium.org, kundaji@chromium.org, mmenke@chromium.org

[sdefresne, 2015-11-21 08:55:59]

kundaji: could you review the following as OWNERS
 - components/data_reduction_proxy

mmenke: could you review the following as OWNERS
 - chrome/browser/io_thread.cc

droger: Please take a look.

[droger, 2015-11-23 08:55:33]

lgtm

[Not at Google. Contact bengr, 2015-11-23 18:15:56]

lgtm

[mmenke, 2015-11-23 18:19:44]

On 2015/11/23 18:15:56, kundaji wrote:
> lgtm

LGTM, thanks for the cleanup!

[sdefresne, 2015-11-24 08:52:00]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-11-24 08:52:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1463973003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1463973003/1

[commit-bot: I haz the power, 2015-11-24 08:58:31]

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

[commit-bot: I haz the power, 2015-11-24 08:58:32]

Try jobs failed on following builders:
  ios_dbg_simulator_ninja on tryserver.chromium.mac (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)

[sdefresne, 2015-11-24 15:13:31]

The CQ bit was checked by sdefresne@chromium.org

[sdefresne, 2015-11-24 15:13:31]

The patchset sent to the CQ was uploaded after l-g-t-m from droger@chromium.org,
kundaji@chromium.org, mmenke@chromium.org
Link to the patchset: https://codereview.chromium.org/1463973003/#ps20001
(title: "Rebase")

[commit-bot: I haz the power, 2015-11-24 15:13:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1463973003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1463973003/20001

[commit-bot: I haz the power, 2015-11-24 16:26:46]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-24 16:28:22]

Patchset 2 (id:??) landed as
https://crrev.com/00e1e6c710ed420e00cf457b5048d813b7a3c2cb
Cr-Commit-Position: refs/heads/master@{#361358}