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/internal/provisional/views/markers/MarkerContentGenerator.java
private void computeMarkers(Collection returnMarkers,
			SubProgressMonitor subMonitor, MarkerFieldFilterGroup filterGroup) {
		int filterType = filterGroup.getScope();
		switch (filterType) {
		case MarkerFieldFilterGroup.ON_ANY: {
			findMarkers(returnMarkers, new IResource[] { ResourcesPlugin
					.getWorkspace().getRoot() }, filterGroup,
					IResource.DEPTH_INFINITE, subMonitor);
			break;
		}
		case MarkerFieldFilterGroup.ON_SELECTED_ONLY: {
			findMarkers(returnMarkers, focusResources, filterGroup,
					IResource.DEPTH_ZERO, subMonitor);
			break;
		}
		case MarkerFieldFilterGroup.ON_SELECTED_AND_CHILDREN: {
			findMarkers(returnMarkers, focusResources, filterGroup,
					IResource.DEPTH_INFINITE, subMonitor);
			break;
		}
		case MarkerFieldFilterGroup.ON_ANY_IN_SAME_CONTAINER: {
			findMarkers(returnMarkers, getProjects(focusResources),
					filterGroup, IResource.DEPTH_INFINITE, subMonitor);
			break;
		}
		case MarkerFieldFilterGroup.ON_WORKING_SET: {
			findMarkers(returnMarkers, getResourcesInWorkingSet(), filterGroup,
					IResource.DEPTH_INFINITE, subMonitor);
		}
		}