Bug 250133 [Contexts] ContextAction's leak when hiding actions sets
bundles/org.eclipse.core.commands/src/org/eclipse/core/commands/contexts/ContextManager.java
* never <code>null</code>.
	 */
	private Set activeContextIds = new HashSet();
	
	private boolean caching = false;
	
	private int cachingRef = 0;
	private boolean activeContextsChange = false;
	
	private Set oldIds = null;
	/**
	 * Activates a context in this context manager.
	 * 
	 * @param contextId
	 *            The identifier of the context to activate; must not be
	 *            <code>null</code>.
	 */
	public final void addActiveContext(final String contextId) {
		if (DEFER_EVENTS.equals(contextId)) {
			cachingRef++;
			if (cachingRef==1) {
				setEventCaching(true);
			}
			return;
		} else if (SEND_EVENTS.equals(contextId)) {
			cachingRef--;
			if (cachingRef==0) {
				setEventCaching(false);
			}
			return;