src/vs/workbench/api/common/extHostOutput.ts/ExtHostOutputService/createOutputChannel
class ExtHostOutputService:	createOutputChannel(name: string, languageId: string | undefined, extension: IExtensionDescription): vscode.OutputChannel {
		name = name.trim();
		if (!name) {
			throw new Error('illegal argument `name`. must not be falsy');
		}
		if (isString(languageId) && !languageId.trim()) {
			throw new Error('illegal argument `languageId`. must not be empty');
		}
		const extHostOutputChannel = this.doCreateOutputChannel(name, languageId, extension);
		extHostOutputChannel.then(channel => {
			this.channels.set(channel.id, channel);
			channel.visible = channel.id === this.visibleChannelId;
		});
		return this.createExtHostOutputChannel(name, extHostOutputChannel);
	}