Bug 221521 [Markers] New markers API needs to be pared down
We have too much API in some of the new classes and they can be moved to internals
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/MarkerContentGenerator.java
private static final String ATTRIBUTE_VISIBLE = "visible"; 
	public static final Object CACHE_UPDATE_FAMILY = new Object();
	private static final String ELEMENT_MARKER_FIELD_FILTER_GROUP = "markerFieldFilterGrouping"; 
	private static final IResource[] EMPTY_RESOURCE_ARRAY = new IResource[0];
	private static final String MARKER_FIELD_REFERENCE = "markerFieldReference"; 
	private MarkerField[] allFields;
	private IConfigurationElement configurationElement;
	private Collection markerTypes;
	private MarkerField[] initialVisible;
	private Collection groups;
	private Collection generatorExtensions = new ArrayList();
	/**
	 * Create a new MarkerContentGenerator
	 * 
	 * @param element
	 */
	public MarkerContentGenerator(IConfigurationElement element) {
		configurationElement = element;
	}
	/**
	 * Add the groups defined in the receiver to the collection of groups.
	 * 
	 * @param groups
	 */
	private void addDefinedGroups(Collection groups) {
		
		addGroupsFrom(configurationElement, groups);
		
		Iterator extensions = generatorExtensions.iterator();
		while (extensions.hasNext()) {