src/vs/workbench/services/workingCopy/common/workingCopyBackupService.ts/NativeWorkingCopyBackupServiceImpl/hasBackupSync
class NativeWorkingCopyBackupServiceImpl:	hasBackupSync(identifier: IWorkingCopyIdentifier, versionId?: number): boolean {
		if (!this.model) {
			return false;
		}

		const backupResource = this.toBackupResource(identifier);

		return this.model.has(backupResource, versionId);
	}