Investigate using headless Chrome for testing Polymer 2 features

[Legioth]

Artur and/or Juhani might have some knowledge about using headless Chrome.

Alternatives:

• Use a standalone Chrome or Firefox
• Transpile Polymer 2 to ES5

[Artur-]

Gut feeling today would be that we should just set up xvfb + Chrome and run with that on Travis instead of PhantomJS.

https://bugs.chromium.org/p/chromium/issues/detail?id=604324 tracks "Selenium support for headless" but likely nothing will happen before https://bugs.chromium.org/p/chromium/issues/detail?id=612904 "Provide a runtime --headless mode for Chrome" lands. The second issue has not had activity this year

[denis-anisimov]

So in the end I think Artur is right.

• Headless Chrome can be used on Linux only (at the moment). I'm not even sure that it can be used at all since I don't have linux. There is a headless_shell which is available right now (not the same as headless chrome but rather some library which does some rendering). It also works on linux only. There is an experimental docker image available https://hub.docker.com/r/justinribeiro/chrome-headless/. I had no chance to check it since I'm not able even to install the docker locally. But it requires Chrome DevTools to communicate with and it's not clear how it's going to work with Selenium at all.
• Transpilation looks too cumbersome. It's possible to transpile but it's not clear at which phase ? Most convenient way would be to transpile on the build phase (e.g. for tests only) and use e.g. maven plugin for that (with a lot of configuration) : http://mabboud.net/how-to-uglify-and-transpile-ecma6-javascript-with-a-maven-war-build/. But more steps are still needed : the result of transpilation are JS files but HTML imports are used in the HB server side code. So there should be additional step which replaces all HTML imports to JS tags..... Quite complicated.
• And the last option: use real Chrome with xvfb. I would say it's most convenient option at the moment. But there are drawbacks : phantomjs is used as a maven plugin at the moment and it doesn't require anything to run the tests. It works out of the box. With Chrome we will have to either require additional not obvious configuration from the user which wants to execute the tests (locally) or we need a way to run the tests using remote Chrome (e.g. via Teamcity). Or both: a way to run the tests locally using local Chrome (if no access to Teamcity) and run tests remotely on Teamcity for those who don't want to configure local execution.