Bug 40788 [plan item] Configurable Next/Previous actions
Toolbar drop down, or editor specific control. Needs to be coordinated with Platform UI.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/JavaEditor.java
}
	/**
	 * Installs the differ annotation model with the current quick diff display. 
	 * @since R3.0
	 */
	private void installChangeRulerModel() {
		IChangeRulerColumn column= getChangeColumn();
		if (column != null)
			column.setModel(getOrCreateDiffer());
	}
	/**
	 * Uninstalls the differ annotation model from the current quick diff display.
	 * 
	 * @since R3.0
	 */
	private void uninstallChangeRulerModel() {
		IChangeRulerColumn column= getChangeColumn();
		if (column != null)
			column.setModel(null);
	}
	/**
	 * Ensures that either the line number display is a <code>LineNumberChangeRuler</code> or
	 * a separate change ruler gets displayed.
	 * 
	 * @since R3.0
	 */
	private void ensureChangeInfoCanBeDisplayed() {
		if (isLineNumberRulerVisible()) {
			if (!(fLineNumberRulerColumn instanceof IChangeRulerColumn)) {
				hideLineNumberRuler();