Bug 214492 [Markers] Need to be able to add filters to existing markers views
Currently you can only add filters to a new markerContentProvider. We need to able to bind them to existing markerContentProviders as well.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/views/markers/internal/MarkerSupportRegistry.java
public static final String MARKER_GROUPING_ENTRY = "markerGroupingEntry"; 
	private static final Object SEVERITY_ID = "org.eclipse.ui.ide.severity";
	/**
	 * The tag for content generators.
	 */
	static final String MARKER_CONTENT_GENERATOR = "markerContentGenerator"; 
	private static final String MARKER_FIELD = "markerField"; 
	private static final String ATTRIBUTE_CLASS = "class"; 
	/**
	 * The bookmarks generator.
	 */
	public static final String BOOKMARKS_GENERATOR = "org.eclipse.ui.ide.bookmarksGenerator"; 
	/**
	 * The tasks generator.
	 */
	public static final String TASKS_GENERATOR = "org.eclipse.ui.ide.tasksGenerator"; 
	/**
	 * The problems generator.
	 */
	public static final String PROBLEMS_GENERATOR = "org.eclipse.ui.ide.problemsGenerator"; 
	/**
	 * The id for the new markers view.
	 */
	public static final String MARKERS_ID = "org.eclipse.ui.ide.MarkersView"; 
	private static MarkerSupportRegistry singleton;
	
	private static Object creationLock = new Object();
	/**
	 * Get the instance of the registry.
	 *