Move preferred scrollbar style preference change listening from renderer to browser, 1 of 3.

This first part just addds a new parameter (via method overloading to keep
compatibility) that will be sent in an IPC from the browser.

BUG=306348

Review URL: https://codereview.chromium.org/142033003

git-svn-id: svn://svn.chromium.org/blink/trunk@165560 bbb929c8-8fbe-4397-9dbb-9b2b20218538