src/vs/platform/userDataSync/common/userDataSyncService.ts/Synchronizers/registerSynchronizer
class Synchronizers:	private registerSynchronizer(syncResource: SyncResource): void {
		if (this._enabled.some(([synchronizer]) => synchronizer.resource === syncResource)) {
			return;
		}
		if (syncResource === SyncResource.Extensions && !this.extensionGalleryService.isEnabled()) {
			this.logService.info('Skipping extensions sync because gallery is not configured');
			return;
		}
		const disposables = new DisposableStore();
		const synchronizer = disposables.add(this.createSynchronizer(syncResource));
		disposables.add(synchronizer.onDidChangeStatus(() => this.onDidChangeStatus(this.enabled)));
		disposables.add(synchronizer.onDidChangeConflicts(() => this.onDidChangeConflicts(this.enabled)));
		disposables.add(synchronizer.onDidChangeLocal(() => this.onDidChangeLocal(syncResource)));
		const order = this.getOrder(syncResource);
		this._enabled.push([synchronizer, order, disposables]);
	}