[CW] [00000] Make ui/tool_tip an anonymous class

- ToolTip subclasses google.maps.OverlayView which isn't always
  available.
- This creates a function within ui/tool_tip which defines the class
  when needed rather than when the file is required (onload).
Merge pull request #4 from primedia/cw/tool_tip_anonymous_class

[CW] [00000] Make ui/tool_tip an anonymous class