src/vs/platform/webview/common/webviewPortMapping.ts/WebviewPortMappingManager/getOrCreateTunnel
class WebviewPortMappingManager:	private async getOrCreateTunnel(remoteAuthority: IAddress, remotePort: number): Promise<RemoteTunnel | undefined> {
		const existing = this._tunnels.get(remotePort);
		if (existing) {
			return existing;
		}
		const tunnel = await this.tunnelService.openTunnel({ getAddress: async () => remoteAuthority }, undefined, remotePort);
		if (tunnel) {
			this._tunnels.set(remotePort, tunnel);
		}
		return tunnel;
	}