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
*/
			int width= getFieldWidth(markerField, -1, treePainted);
			columnEntry.putInteger(getFieldId(column), width);
			fields[positions[i]]= markerField;
		}
		if (generator != null) {
			generator.saveState(memento, fields);
		}
		builder.saveState(memento);
	}
	/**
	 * Select all of the elements in the receiver.
	 */
	void selectAll() {
		viewer.getTree().selectAll();
	}
	/**
	 * Set the category group for the receiver.
	 * 
	 * @param group
	 */
	void setCategoryGroup(MarkerGroup group) {
		getCategoriesToExpand().clear();
		builder.setCategoryGroup(group);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.ui.part.WorkbenchPart#setFocus()
	 */