Bug 205049 Other plug-ins should be able to define default content generator
Currently only the content generator can define which plug-ins it can be the default for - we need a way for plug-ins to refer back to the marker support for thier own generator.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/views/markers/internal/MarkerSupportRegistry.java
}
	/**
	 * Return the FieldMarkerGroups in the receiver.
	 * 
	 * @return Collection of {@link MarkerGroup}
	 */
	public Collection getMarkerGroups() {
		return markerGroups.values();
	}
	/**
	 * Return the default groupfield.
	 * 
	 * @return IField
	 */
	IField getDefaultGroupField() {
		return ((MarkerGroup) markerGroups.get(SEVERITY_ID)).getField();
	}
	/**
	 * Get the generator for id
	 * 
	 * @param id
	 * @return MarkerContentGenerator or <code>null</code>.
	 */
	public MarkerContentGenerator getGenerator(String id) {
		if (id != null && generators.containsKey(id))
			return (MarkerContentGenerator) generators.get(id);
		return null;
	}
	/**
	 * Return the generator for the supplied perspective.