Bug 219909 [DataBinding] UnmodifiableObservableValue
UnmodifiableObservableValue with test cases
bundles/org.eclipse.core.databinding/src/org/eclipse/core/databinding/observable/Observables.java
* returned list continues to work after it has been disposed of and can be
	 * disposed of multiple times.
	 * 
	 * @param realm
	 *            the realm of the returned list
	 * @return an empty observable list.
	 */
	public static IObservableList emptyObservableList(Realm realm) {
		return emptyObservableList(realm, null);
	}
	/**
	 * Returns an empty observable list of the given element type and belonging
	 * to the given realm. The returned list continues to work after it has been
	 * disposed of and can be disposed of multiple times.
	 * 
	 * @param realm
	 *            the realm of the returned list
	 * @param elementType
	 *            the element type of the returned list
	 * @return an empty observable list
	 * @since 1.1
	 */
	public static IObservableList emptyObservableList(Realm realm,
			Object elementType) {
		return new EmptyObservableList(realm, elementType);
	}
	/**
	 * Returns an empty observable set. The returned set continues to work after
	 * it has been disposed of and can be disposed of multiple times.
	 *