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
if (scope.equals(ON_ANY)) {
			return MarkerFilter.ON_ANY;
		}
		if (scope.equals(ON_SELECTED_ONLY)) {
			return MarkerFilter.ON_SELECTED_ONLY;
		}
		if (scope.equals(ON_SELECTED_AND_CHILDREN)) {
			return MarkerFilter.ON_SELECTED_AND_CHILDREN;
		}
		if (scope.equals(ON_ANY_IN_SAME_CONTAINER)) {
			return MarkerFilter.ON_ANY_IN_SAME_CONTAINER;
		}
		return -1;
	}
	/**
	 * Get the constant for scope from element. Return -1 if there is no value.
	 * 
	 * @param element
	 * @return int one of MarkerView#ON_ANY MarkerView#ON_SELECTED_ONLY
	 *         MarkerView#ON_SELECTED_AND_CHILDREN
	 *         MarkerView#ON_ANY_IN_SAME_CONTAINER
	 */
	private int getSeverityValue(IConfigurationElement element) {
		String severity = element.getAttribute(SEVERITY);
		if (severity == null) {
			return -1;
		}
		if (severity.equals(INFO)) {
			return ProblemFilter.SEVERITY_INFO;
		}