Move preferred scrollbar style preference change listening from renderer to browser, 2 of 3.

Move preferred scrollbar style preference change listening from renderer to browser, 2 of 3.

This adds the preference observer to the browser and starts sending the
parameter to the renderer over IPC when it changes. Blink will not use this
until part 3 lands.

BUG=306348
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=246635

[Robert Sesek, 2014-01-17 21:35:53]

Part 1: https://codereview.chromium.org/142033003/
Part 3: https://codereview.chromium.org/136333009/

[Avi (use Gerrit), 2014-01-20 22:53:33]

LGTM

[Robert Sesek, 2014-01-22 23:00:24]

+tsepez for content/common/view_messages.h
+jamesr to approve OWNERS for introducing a DEPS change from content on
WebKit/public (the enum value from https://codereview.chromium.org/142033003/)

[jamesr, 2014-01-22 23:02:02]

DEPS change lgtm

[Tom Sepez, 2014-01-22 23:04:27]

Messages LGTM.

[commit-bot: I haz the power, 2014-01-23 14:02:06]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rsesek@chromium.org/136443008/60001

[commit-bot: I haz the power, 2014-01-23 14:39:54]

Retried try job too often on ios_dbg_simulator for step(s) base_unittests,
compile, content_unittests, crypto_unittests, net_unittests, sql_unittests,
ui_unittests, url_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=ios_dbg_si...

[commit-bot: I haz the power, 2014-01-23 14:41:22]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rsesek@chromium.org/136443008/60001

[commit-bot: I haz the power, 2014-01-23 15:09:18]

Retried try job too often on ios_dbg_simulator for step(s) base_unittests,
compile, content_unittests, crypto_unittests, net_unittests, sql_unittests,
ui_unittests, url_unittests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=ios_dbg_si...

[commit-bot: I haz the power, 2014-01-23 15:25:31]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rsesek@chromium.org/136443008/590001

[commit-bot: I haz the power, 2014-01-23 15:49:29]

Failed to get patchset properties (patchset not found?)

[commit-bot: I haz the power, 2014-01-23 15:51:30]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rsesek@chromium.org/136443008/760001

[commit-bot: I haz the power, 2014-01-23 17:49:14]

Change committed as 246635