Bug 189490 [CommonNavigator] Go To->Resource won't enable
I0524 1. Open the Project Explorer in the Resource perspective 2. Create a vanilla project P 3. Create a folder F 4. Create a file resource R Open the Navigate->Go To file. "Resource..." will remain disabled.
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/NavigatorContentService.java
*            The descriptor of the extension that contributed the set of
	 *            elements.
	 * @param element
	 *            An element from the given source.
	 */
	public synchronized void rememberContribution(
			NavigatorContentDescriptor source, Object element) {
		Map memory = getContributionMemory();
		if (element != null) {
			if (memory.containsKey(element))
				return;
			if (source != null)
				memory.put(element, source);
		}
	}
	/**
	 * Forget about the specified element
	 * 
	 * @param element
	 *            The element to forget.
	 */
	public synchronized void forgetContribution(Object element) {
		if (element != null)
			getContributionMemory().remove(element);
	}
	/**
	 * 
	 * @param element
	 *            The element contributed by the descriptor to be returned
	 * @return The descriptor that contributed the element or null.