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
* 
	 * @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 default content generator.
	 * 
	 * @return MarkerContentGenerator
	 */
	public MarkerContentGenerator getDefaultGenerator() {
		return (MarkerContentGenerator) generators.get(PROBLEMS_GENERATOR);
	}
	/**
	 * Get the markerGroup associated with categoryName
	 * 
	 * @param categoryName
	 * @return FieldMarkerGroup or <code>null</code>