src/vs/platform/userDataSync/common/abstractSynchronizer.ts/isSyncData
export function isSyncData(thing: any): thing is ISyncData {
	if (thing
		&& (thing.version !== undefined && typeof thing.version === 'number')
		&& (thing.content !== undefined && typeof thing.content === 'string')) {

		// backward compatibility
		if (Object.keys(thing).length === 2) {
			return true;
		}

		if (Object.keys(thing).length === 3
			&& (thing.machineId !== undefined && typeof thing.machineId === 'string')) {
			return true;
		}
	}

	return false;
}