Bug 241209 [Markers] [Problems View] Changing columns in the preferences makes errors disappear from the view
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/ExtendedMarkersView.java
*/
			public Object getParent(Object element) {
				Object parent = ((MarkerSupportItem) element).getParent();
				if (parent == null)
					return builder;
				return parent;
			}
			/*
			 * (non-Javadoc)
			 * 
			 * @see org.eclipse.jface.viewers.ITreeContentProvider#hasChildren(java.lang.Object)
			 */
			public boolean hasChildren(Object element) {
				return ((MarkerSupportItem) element).getChildren().length > 0;
			}
			/*
			 * (non-Javadoc)
			 * 
			 * @see org.eclipse.jface.viewers.IContentProvider#inputChanged(org.eclipse.jface.viewers.Viewer,
			 *      java.lang.Object, java.lang.Object)
			 */
			public void inputChanged(Viewer viewer, Object oldInput,
					Object newInput) {
			}
		};
	}
	/**
	 * Get the id of the marker field in treeColumn.
	 * 
	 * @param treeColumn