src/vs/platform/userDataSync/common/abstractSynchronizer.ts/AbstractInitializer/updateLastSyncUserData
class AbstractInitializer:	protected async updateLastSyncUserData(lastSyncRemoteUserData: IRemoteUserData, additionalProps: IStringDictionary<any> = {}): Promise<void> {
		if (additionalProps['ref'] || additionalProps['version']) {
			throw new Error('Cannot have core properties as additional');
		}

		const lastSyncUserDataState: ILastSyncUserDataState = {
			ref: lastSyncRemoteUserData.ref,
			version: undefined,
			...additionalProps
		};

		this.storageService.store(`${this.resource}.lastSyncUserData`, JSON.stringify(lastSyncUserDataState), StorageScope.APPLICATION, StorageTarget.MACHINE);
		await this.fileService.writeFile(this.lastSyncResource, VSBuffer.fromString(JSON.stringify(lastSyncRemoteUserData)));
	}