src/vs/workbench/api/node/extHostTunnelService.ts/ExtHostTunnelService/openTunnel
class ExtHostTunnelService:	async openTunnel(extension: IExtensionDescription, forward: TunnelOptions): Promise<vscode.Tunnel | undefined> {
		this.logService.trace(`ForwardedPorts: (ExtHostTunnelService) ${extension.identifier.value} called openTunnel API for ${forward.remoteAddress.host}:${forward.remoteAddress.port}.`);
		const tunnel = await this._proxy.$openTunnel(forward, extension.displayName);
		if (tunnel) {
			const disposableTunnel: vscode.Tunnel = new ExtensionTunnel(tunnel.remoteAddress, tunnel.localAddress, () => {
				return this._proxy.$closeTunnel(tunnel.remoteAddress);
			});
			this._register(disposableTunnel);
			return disposableTunnel;
		}
		return undefined;
	}