Move preferred scrollbar style preference change listening from renderer to browser, 4 of 3.

Move preferred scrollbar style preference change listening from renderer to browser, 4 of 3.

When --single-process, do not broker system notifications to renderers, since it
will cause some content_browsertests to DCHECK.

BUG=306348
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=247030

[Avi (use Gerrit), 2014-01-24 21:12:23]

I just realized that this solves the problem for the cases where the Imps listen
for the notification themselves, but technically it breaks the case where the
scrollers don't (the existing code). This might break scroller changes in single
process. I don't really care.

LGTM

[Robert Sesek, 2014-01-24 21:20:49]

On 2014/01/24 21:12:23, Avi wrote:
> I just realized that this solves the problem for the cases where the Imps
listen
> for the notification themselves, but technically it breaks the case where the
> scrollers don't (the existing code). This might break scroller changes in
single
> process. I don't really care.
> 
> LGTM

I guess it's not hard to _not_ break that. PTAL.

[Avi (use Gerrit), 2014-01-24 22:17:01]

SLGTM.

[commit-bot: I haz the power, 2014-01-24 22:27:11]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rsesek@chromium.org/145013018/60001

[commit-bot: I haz the power, 2014-01-25 00:20:12]

Change committed as 247030