Tell the root layer it has a wheel handler when a select is open

Otherwise, the input events are handled in
content::InputHandlerProxy::HandleInputEvent and not forwarded to the
renderer, so the select popup is not closed when wheeling over the main
content.

R=jamesr@chromium.org
BUG=294506

Review URL: https://chromiumcodereview.appspot.com/23677012

git-svn-id: svn://svn.chromium.org/blink/trunk@158148 bbb929c8-8fbe-4397-9dbb-9b2b20218538