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

Review URL: https://codereview.chromium.org/145013018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247030 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed