Support for User-Agent based rendered apps about lighthouse

[brendankenny]

Hi Boopathi!

Right now lighthouse uses the debugging protocol to always enter device mode emulation when testing. The code for this is in emulation.js and is called from the protocol driver. This exact device parameters are hard coded right now, but this could eventually be configurable. @paulirish has probably already been thinking about what we're going to do here.

The manifest fetching issue is going to be fixed by having the page itself fetch the manifest and swiping it from the network traffic. This is tracked in #83

[paulirish]

Looks like DevTools and lighthouse(extension) debugger cannot be open at the same time

yup that's true.

So device mode emulation with lighthouse extension seems not possible

it's very possible. so possible that we're already doing it, as brendan pointed out. :)

really the only problem right now is that the manifest is not fetched by the browser while under emulation. That's a bug in lighthouse, and one that we gotta fix asap.

As such, I think this issue mostly gets duped into #83.

[boopathi]

Thanks.

Correct me if I missed something.

The device mode emulation is done when you invoke the extension. So we'd have to reload the app after device mode is turned on - i.e. when the lighthouse extension is invoked - right ?

Or you'd have to open dev tools, enable device mode emulation, reload/load the app. Close devtools. Use extension.

[paulirish]

Ah! good call yeah.

If the content is dependent on the UA, then yeah a reload will be neccessary. Right now extension can't reload the page but that's what's happening in #52. Take a look on that issue and see if the user flow that makes sense to you.