DOMUI Prefs: Implement inline editability for startup pages
Also moves more common code into InlineEditableItem, and fixes some styling issues with inline-editable lists.
BUG=
63817
TEST=Startup pages should be editable in DOMUI prefs. Also, the lead selection in an editable list should show top and bottom borders.
Committed:
http://src.chromium.org/viewvc/chrome?view=rev&revision=71464