How to add a menu item to the File Tab context menu in a VSIX package?

I'd like to add a menu item for the context menu which appears for the File tab in Visual Studio 2013 (the one that has items like Close All Documents, Copy Full Path, Open Containing Folder, etc).

I have a VSIX project, and would assume that all I need to do is to get the right service (via GetService). But I have no idea what the name of the correct service is.