public interface DebuggerBreakpointGutterToggleHandler
Interface used by debugger extenders when they want to control the
type of breakpoint created when the user clicks in the gutter of a
code editor page to create a breakpoint.
In order for this interface to be called, extender must register a
<debugger-gutter-click-toggle-handler> will the 'class' attribute pointing
to a class that implements this interface, and the 'node-class' attibute identifying
the fully-qualified name of a Node type for which the handler should be invoked.