Bug 279452 [Compatibility] Parameterized command mechanism support
Parameterized commands like showView need to be able to access their parameters (like the view ID) PW
bundles/org.eclipse.e4.ui.services/src/org/eclipse/e4/ui/internal/services/ContextHandlerService.java
Object rc = factory.call(handler, null, "canExecute", context,
				Boolean.TRUE);
		if (Boolean.FALSE.equals(rc)) {
			return null;
		}
		return factory.call(handler, null, "execute", context, null);
	}
	public void deactivateHandler(String commandId, Object handler) {
		Object object = context.get(PREFIX + commandId);
		if (object == handler) {
			context.remove(PREFIX + commandId);
		}
	}
	public boolean canExecute(String commandId) {
		Object handler = context.get(commandId, new Object[] { "handler" });
		if (handler == null) {
			return false;
		}
		IContributionFactory factory = (IContributionFactory) context.get(
				"org.eclipse.e4.core.services.IContributionFactory",
				new Object[] { handler });
		Object rc = factory.call(handler, null, "canExecute", context,
				Boolean.TRUE);
		if (Boolean.FALSE.equals(rc)) {
			return false;
		}
		return true;
	}
}