Export Chromium BrowserType implementation directly

[imiric]

In #462 we made a chromium object importable in scripts, but the way it's done is a bit convoluted:

xk6-browser/main.go

Lines 61 to 68 in aadaffe

	func (mi *ModuleInstance) Exports() k6modules.Exports {
	return k6modules.Exports{
	Named: map[string]interface{}{
	"chromium": mi.mod,
	"devices": mi.mod.Devices,
	},
	}
	}

That is, "chromium" actually points to the JSModule itself, and calling chromium.launch() calls the module-level Launch() wrapper, which internally creates a Chromium BrowserType and calls BrowserType.Launch().

Which means this is possible:

import { chromium } from 'k6/x/browser';

export default function() {
  // logs v0.4.0, the xk6-browser version, not the Chromium version
  console.log(chromium.version);
  // logs the device configuration map, which should be browser-agnostic
  console.log(chromium.devices);
}

Suggested solution

As mentioned here and here, import { chromium } from 'k6/x/browser'; should actually import the Chromium BrowserType instance directly, so the script can call all of its public methods. This would allow us to easily support other BrowserType implementations in the future.

And if the user wants access to module-level attributes, the script should import the module instead, e.g. import k6b from 'k6/x/browser;.