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
MarkerGroupingEntry entry = new MarkerGroupingEntry(element);
				String groupName = element.getAttribute(MARKER_GROUPING);
				Collection entries;
				if (groupIDsToEntries.containsKey(groupName)) {
					entries = (Collection) groupIDsToEntries.get(groupName);
				} else {
					entries = new HashSet();
				}
				entries.add(entry);
				groupIDsToEntries.put(groupName, entries);
				entryIDsToEntries.put(entry.getId(), entry);
				tracker.registerObject(extension, entry,
						IExtensionTracker.REF_STRONG);
				continue;
			}
			if (element.getName().equals(MARKER_ATTRIBUTE_GROUPING)) {
				AttributeMarkerGrouping grouping = new AttributeMarkerGrouping(element);
				attributeMappings.add(grouping);
				tracker.registerObject(extension, grouping,
						IExtensionTracker.REF_STRONG);
				continue;
			}
			if (element.getName().equals(MARKER_CATEGORY)) {
				String[] markerTypes = getMarkerTypes(element);
				String categoryName = element
						.getAttribute(MarkerSupportConstants.ATTRIBUTE_NAME);
				for (int i = 0; i < markerTypes.length; i++) {
					categories.put(markerTypes[i], categoryName);
				}
				tracker.registerObject(extension, categoryName,