It is not available from Extension Warehouse but is at (we are evaluating an alternative plugin called Guide Tools available at )
Here are some recommended extensions as an update to those previously assembled here. There is an Extension Warehouse that can be called by clicking on the button (below) located on the toolbar.
Trimble SketchUp now hosts a repository for SketchUp plugins that one can access and install directly from SketchUp Make or Pro. As mentioned previously, SketchUp 2014 has a new scheme for installing plugins.