Support async protractor config

[Amy-Lynn]

Feature Request

In protractor.conf.js, allow the export to be either a config object (current behavior) or a promise that resolves to the config object.

• Reasons for adopting new feature I'm running an electron app, so using Spectron to launch the app. I can start the app and get a selenium session id, but that's asynchronous. While you can start protractor in a new process and pass in the sessionId via CLI, then I don't have access to the Spectron object (so I lose electron-specific functionality). This would also address #4749
• Is this a breaking change? (How will this affect existing functionality) Shouldn't be breaking (unless you have an existing config

Happy to try a PR.

[troppoli]

I was looking for more information about starting spectron within a protractor process. It seems that you did that with some success. The config for protractor seems to want the selenium session id at launch, I saw that there is a beforeLaunch hook that I was thinking might be a place to boot spectron and get the seleniumSessionId setup as well as stuffing the spectron object into browser for later use. Did you try that approach?

[troppoli]

here's where I ended up, seems to work. I expect that I could add app to the the 'params' object and that would be available in the tests.

import {Config} from 'protractor';
import { Application } from 'spectron';

let app:Application;

export let config: Config = {
    framework: 'jasmine',
    specs:['something_spec.js'],
    seleniumAddress:'http://localhost:9515/wd/hub',
    beforeLaunch: async()=>{
        app = new Application({
            path: 'PATH_TO_ELECTRON_APP.exe',
            webdriverLogPath:'c:\\temp\\webdriverlog.log'
          })
          await app.start();
          let s:any = await app.client.session();
          config.seleniumSessionId = s.sessionId;
    },
    afterLaunch: async (exitCode: number) =>{
        return app.stop();
    }
};