src/vs/workbench/services/workingCopy/common/workingCopyBackupService.ts/InMemoryWorkingCopyBackupService/backup
class InMemoryWorkingCopyBackupService:	async backup(identifier: IWorkingCopyIdentifier, content?: VSBufferReadable | VSBufferReadableStream, versionId?: number, meta?: IWorkingCopyBackupMeta, token?: CancellationToken): Promise<void> {
		const backupResource = this.toBackupResource(identifier);
		this.backups.set(backupResource, {
			typeId: identifier.typeId,
			content: content instanceof VSBuffer ? content : content ? isReadableStream(content) ? await streamToBuffer(content) : readableToBuffer(content) : VSBuffer.fromString(''),
			meta
		});
	}