Bug 139986 [CommonNavigator] Convert catch(Error/Throwable) to SafeRunner
In several places the CN framework uses catch(Error/Throwable) to ensure that code does not bring the framework down. Change these to use SafeRunner.
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/internal/navigator/extensions/NavigatorContentDescriptorManager.java
/**
	 * 
	 * Returns all content descriptor(s) which enable for the given element.
	 * 
	 * @param anElement
	 *            the element to return the best content descriptor for
	 * 
	 * @param aVisibilityAssistant
	 *            The relevant viewer assistant; used to filter out unbound
	 *            content descriptors.
	 * @param considerOverrides 
	 * @return the best content descriptor for the given element.
	 */
	public Set findDescriptorsForTriggerPoint(Object anElement,
			VisibilityAssistant aVisibilityAssistant, boolean considerOverrides) {
		return findDescriptors(anElement, cachedTriggerPointEvaluations, aVisibilityAssistant, considerOverrides, !POSSIBLE_CHILD);
	}
	/**
	 * 
	 * Returns all content descriptor(s) which enable for the given element.
	 * 
	 * @param anElement
	 *            the element to return the best content descriptor for
	 * 
	 * @param aVisibilityAssistant
	 *            The relevant viewer assistant; used to filter out unbound
	 *            content descriptors.
	 * @param toComputeOverrides
	 * @return the best content descriptor for the given element.
	 */