Bug 218884 [DataBinding] Add API: WorkbenchObservables
... for things like listening to ISelectionService
bundles/org.eclipse.core.databinding.observable/src/org/eclipse/core/databinding/observable/Observables.java
*            the delay in milliseconds
	 * @param observable
	 *            the observable being delayed
	 * @return an observable which delays notification of value change events
	 *         from <code>observable</code> until <code>delay</code>
	 *         milliseconds have elapsed since the last change event.
	 * 
	 * @since 1.2
	 */
	public static IObservableValue observeDelayedValue(int delay,
			IObservableValue observable) {
		return new DelayedObservableValue(delay, observable);
	}
	/**
	 * Returns an unmodifiable observable value backed by the given observable
	 * value.
	 * 
	 * @param value
	 *            the value to wrap in an unmodifiable value
	 * @return an unmodifiable observable value backed by the given observable
	 *         value
	 * @since 1.1
	 */
	public static IObservableValue unmodifiableObservableValue(
			IObservableValue value) {
		Assert.isNotNull(value, "Argument 'value' cannot be null"); 
		return new UnmodifiableObservableValue(value);
	}
	/**
	 * Returns an observable value with the given constant value.