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
entries = new HashSet();
				}
				entries.add(entry);
				groupingEntries.put(groupName, entries);
				tracker.registerObject(extension, entry,
						IExtensionTracker.REF_STRONG);
				continue;
			}
			if (element.getName().equals(MARKER_ATTRIBUTE_GROUPING)) {
				AttributeMarkerGrouping grouping = new AttributeMarkerGrouping(
						element.getAttribute(ATTRIBUTE), element
								.getAttribute(MARKER_TYPE), element
								.getAttribute(DEFAULT_GROUPING_ENTRY), 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,
						IExtensionTracker.REF_STRONG);
				continue;
			}
			if (element.getName().equals(MARKER_CONTENT_GENERATOR)) {