Bug 274236 [CommonNavigator] Incorrect check for existence of item in contribution memory
The check in the NavigatorContentService.rememberContribution() should be containsKey(), not containsValue()
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
*         <i>visible</i> and <i>active</i> for this content service and
	 *         have a <b>possibleChildren</b> expression that is <i>enabled</i>
	 *         for the given element.
	 */
	public Set findDescriptorsWithPossibleChild(Object anElement,
			boolean toComputeOverrides) {
		
		Set result = new TreeSet(ExtensionPriorityComparator.INSTANCE);
		result.addAll(CONTENT_DESCRIPTOR_REGISTRY
				.findDescriptorsForPossibleChild(anElement, assistant,
						toComputeOverrides));
		return result;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @seeorg.eclipse.ui.internal.navigator.INavigatorContentService#
	 * onExtensionActivation(java.lang.String, java.lang.String, boolean)
	 */
	public void onExtensionActivation(String aViewerId,
			String[] aNavigatorExtensionId, boolean toEnable) {
		synchronized (this) {
			try {
				NavigatorContentDescriptor key;
				NavigatorContentExtension extension;
				for (Iterator iter = contentExtensions.keySet().iterator(); iter
						.hasNext();) {
					key = (NavigatorContentDescriptor) iter.next();
					INavigatorActivationService activation = getActivationService();
					if (!activation.isNavigatorExtensionActive(key.getId())) {