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
c.addDecorator(1, createLineNumberRulerColumn());
		}
	}
	
	/**
	 * Hides the line number ruler column.
	 */
	private void hideLineNumberRuler() {
		IVerticalRuler v= getVerticalRuler();
		if (fLineNumberRulerColumn != null && v instanceof CompositeRuler) {
			CompositeRuler c= (CompositeRuler) v;
			c.removeDecorator(fLineNumberRulerColumn);
			fLineNumberRulerColumn= null;
		}
		if (fIsChangeInformationShown)
			showChangeRuler(true);
	}
	
	/**
	 * Return whether the line number ruler column should be 
	 * visible according to the preference store settings.
	 * 
	 * @return <code>true</code> if the line numbers should be visible
	 */
	private boolean isLineNumberRulerVisible() {
		IPreferenceStore store= getPreferenceStore();
		return store.getBoolean(LINE_NUMBER_RULER);
	}
	
	/**