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
private static final Object WARNING = "WARNING";
	private static final String MARKER_ID = "markerId"; 
	/**
	 * The tag for the marker support extension
	 */
	public static final String MARKER_SUPPORT = "markerSupport";
	private static final Object ON_ANY = "ON_ANY"; 
	private static final Object ON_ANY_IN_SAME_CONTAINER = "ON_ANY_IN_SAME_CONTAINER";
	private static final Object ON_SELECTED_AND_CHILDREN = "ON_SELECTED_AND_CHILDREN";
	private static final Object ON_SELECTED_ONLY = "ON_SELECTED_ONLY"; 
	private static final Object PROBLEM_FILTER = "problemFilter";
	private static final String SCOPE = "scope"; 
	private static final String SELECTED_TYPE = "selectedType"; 
	private static final String SEVERITY = "severity";
	/**
	 * The key for marker type references.
	 */
	public static final String MARKER_TYPE_REFERENCE = "markerTypeReference"; 
	/**
	 * The key for marker support references.
	 */
	public static final String MARKER_SUPPORT_REFERENCE = "markerSupportReference"; 
	private static final String MARKER_CATEGORY = "markerTypeCategory";
	private static final String ATTRIBUTE_MAPPING = "markerAttributeMapping"; 
	/**
	 * The tag for marker grouping.
	 */
	public static final String MARKER_GROUPING = "markerGrouping"; 
	private static final String ATTRIBUTE = "attribute"; 
	private static final String VALUE = "value";