Bug 275910 [Widgets] PaintListener on Tree not invoked when item count is 0
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/views/markers/ExtendedMarkersView.java
public void setFocus() {
		viewer.getControl().setFocus();
	}
	/**
	 * Set the primary sort field
	 * 
	 * @param field
	 */
	void setPrimarySortField(MarkerField field) {
		TreeColumn[] columns = viewer.getTree().getColumns();
		for (int i = 0; i < columns.length; i++) {
			TreeColumn treeColumn = columns[i];
			if (columns[i].getData(MARKER_FIELD).equals(field)) {
				setPrimarySortField(field, treeColumn);
				return;
			}
		}
		StatusManager.getManager().handle(
				StatusUtil.newStatus(IStatus.WARNING,
						"Sorting by non visible field " 
								+ field.getName(), null));
	}
	/**
	 * Set the primary sort field to field and update the column.
	 * 
	 * @param field
	 * @param column
	 */
	private void setPrimarySortField(MarkerField field, TreeColumn column) {
		builder.setPrimarySortField(field);