src/vs/workbench/browser/parts/activitybar/activitybarPart.ts/ActivitybarPart/getCumulativeNumberBadge
class ActivitybarPart:	private getCumulativeNumberBadge(activityCache: ICompositeActivity[], priority: number): NumberBadge {
		const numberActivities = activityCache.filter(activity => activity.badge instanceof NumberBadge && activity.priority === priority);
		const number = numberActivities.reduce((result, activity) => { return result + (<NumberBadge>activity.badge).number; }, 0);
		const descriptorFn = (): string => {
			return numberActivities.reduce((result, activity, index) => {
				result = result + (<NumberBadge>activity.badge).getDescription();
				if (index < numberActivities.length - 1) {
					result = `${result}\n`;
				}

				return result;
			}, '');
		};

		return new NumberBadge(number, descriptorFn);
	}