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
return new IObservableFactory() {
			public IObservable createObservable(Object key) {
				return observeMapEntry(map, key, valueType);
			}
		};
	}
	/**
	 * Helper method for <code>MasterDetailObservables.detailValue(master,
	 * mapEntryValueFactory(map, valueType), valueType)</code>.
	 * 
	 * @param map
	 *            the observable map whose entry will be tracked.
	 * @param master
	 *            the observable value that identifies which map entry to track.
	 * @param valueType
	 *            the type of the value. May be <code>null</code>, meaning
	 *            the value is untyped.
	 * @return an observable value tracking the current value of the specified
	 *         key in the given map an observable value that tracks the current
	 *         value of the named property for the current value of the master
	 *         observable value
	 * @since 1.1
	 */
	public static IObservableValue observeDetailMapEntry(IObservableMap map,
			IObservableValue master, Object valueType) {
		return MasterDetailObservables.detailValue(master,
				mapEntryValueFactory(map, valueType), valueType);
	}
}