WebappInstallBanner should depend on WorksOffline and LoadFastEnough4Pwa

[slightlyoff]

We have always said that one of the most important aspects of "PWAness" is that these experiences meet the expectations of users when it comes to reliably fast loading.

Therefore, I'd like for our "installability" check to be gated on working offline and loading fast enough.

We're going to continue to raise the bar to this level on the Chrome (product) side, so LH getting there first would be a huge help.

Thanks!

[patrickhulce]

The good news the audit is already gated on a stricter criteria than working offline audit, the start URL must work offline.

lighthouse/lighthouse-core/audits/webapp-install-banner.js

Lines 90 to 112 in a99c07b

	/**
	* @param {LH.Artifacts} artifacts
	* @return {{failures: Array<string>, warnings: Array<string>}}
	*/
	static assessOfflineStartUrl(artifacts) {
	const failures = [];
	const warnings = [];
	const hasOfflineStartUrl = artifacts.StartUrl.statusCode === 200;
	if (!hasOfflineStartUrl) {
	failures.push('Service worker does not successfully serve the manifest\'s start_url');
	// TODO(phulce): align gatherer `debugString` with `explanation`
	if (artifacts.StartUrl.debugString) {
	failures.push(artifacts.StartUrl.debugString);
	}
	}
	if (artifacts.StartUrl.debugString) {
	warnings.push(artifacts.StartUrl.debugString);
	}
	return {failures, warnings};
	}

Loading fast enough is being considerably bumped in #5233 so the category won't be green until the app is fast enough. Visual badging needs discussion :)

[slightlyoff]

Ah! I hadn't understood that it tested this rather than just looking for a match on the scope. Great!

Who needs to be involved to make the call on visual badging?

[slightlyoff]

/cc @vinamratasingal

[paulirish]

duping into #5930