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/MarkerGroup.java
if (item1.getMarker() == null) {
				if (item2.getMarker() == null)
					return 0;
				return 1;
			}
			
			if (item2.getMarker() == null)
				return -1;
			try {
				return (findGroupValue(item2.getMarker().getType(),
						item2.getMarker()).getPriority() - findGroupValue(
						item1.getMarker().getType(), item1.getMarker())
						.getPriority());
			} catch (CoreException exception) {
				MarkerSupportInternalUtilities.handle(exception);
				return 0;
			}
		}
		/*
		 * (non-Javadoc)
		 * 
		 * @see org.eclipse.ui.internal.provisional.views.markers.api.MarkerField#getColumnHeaderText()
		 */
		public String getColumnHeaderText() {
			return markerGroup.getTitle();
		}
	}
	private static MarkerGroupingEntry undefinedEntry = new MarkerGroupingEntry(
			MarkerMessages.FieldCategory_Uncategorized);