artifact: fetch manifest based on triggered network request

[brendankenny]

Calling requestAppBanner will fetch the manifest, which we can pick up in the network requests record.

This avoids the DOM dance and make sure we're testing the same manifest that Chrome does.

for now you need --enable-add-to-shelf for this to work

[paulirish]

Once https://codereview.chromium.org/1835063002/ lands, enable-add-to-shelf will not be required.
Star https://bugs.chromium.org/p/chromium/issues/detail?id=540491 for updates.

In the meantime, we can force the flag for node, but not for extension.

We might want to consider requiring Canary for using the extension. (Otherwise we'll be waiting for fixes like this to hit stable)

[paulirish]

This will also mean we can clean up the depedency on request and the localized requires here

[paulirish]

Okay another bug we'll get resolved... on https://operasoftware.github.io/pwa-list/ things fail because it's in a subfolder and our browser fetching assumes manifest is at domain root.

There's a fix for it but I think I'd rather rely on the real thing.

[paulirish]

@brendankenny when do you think you'll have a PR up for this?

[brendankenny]

Aiming for tomorrow

[paulirish]

@brendankenny sounds good thank ya

[brendankenny]

so, one additional development here seems to be that in Canary, if you have Add to shelf enabled in about:flags, Chrome now fetches the manifest on navigation. Is this coming sooner than we expected?

[paulirish]

try https://jakearchibald.github.io/svgomg/ with your PR. i get invalid JSON errors with the extension currently.