RenderListBox should scroll to the selection option upon creation

When a <select multiple> attaches it doesn't scroll to the selected option,
instead options expect to be able to call scrollToSelection() inside
HTMLOptionElement::insertedInto which only works if the select already has
a renderer. Instead we should just always scroll to the selected option
when the RenderListBox is created.

This makes us match Firefox and old Opera behavior as well and gives a much
better user experience since now when a <select> is reattached() it'll scroll
down to the selected option instead of starting at the top.

BUG=276687

Review URL: https://chromiumcodereview.appspot.com/22914025

git-svn-id: svn://svn.chromium.org/blink/trunk@156524 bbb929c8-8fbe-4397-9dbb-9b2b20218538