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/internal/views/markers/MarkerContentGenerator.java
* 
	 * @return {@link MarkerField}[]
	 */
	MarkerField[] getInitialVisible() {
		return initialVisible;
	}
	/**
	 * Get the group called groupName from the receiver
	 * 
	 * @param groupName
	 * @return MarkerGroup or <code>null</code>
	 */
	MarkerGroup getMarkerGroup(String groupName) {
		Iterator groups = getMarkerGroups().iterator();
		while (groups.hasNext()) {
			MarkerGroup group = (MarkerGroup) groups.next();
			if (group.getId().equals(groupName))
				return group;
		}
		return null;
	}
	/**
	 * Get the markerGroups associated with the receiver.
	 * 
	 * @return Collection of {@link MarkerGroup}
	 */
	Collection getMarkerGroups() {
		if (groups == null) {
			groups = new HashSet();