src/vs/platform/userDataSync/common/userDataSyncService.ts/ManualSyncTask/merge
class ManualSyncTask:	async merge(resource?: URI): Promise<[SyncResource, ISyncResourcePreview][]> {
		try {
			if (resource) {
				return await this.performAction(resource, sychronizer => sychronizer.merge(resource));
			} else {
				return await this.mergeAll();
			}
		} catch (error) {
			this.logService.error(error);
			throw error;
		}
	}