src/vs/workbench/services/userDataSync/browser/userDataSyncWorkbenchService.ts/UserDataSyncPreview/cancel
class UserDataSyncPreview:	async cancel(): Promise<void> {
		if (!this.manualSync) {
			throw new Error('Can cancel only while syncing manually');
		}
		await this.manualSync.task.stop();
		this.updatePreview([]);
		this._onDidCompleteManualSync.fire(canceled());
	}