core(lightwallet): add timing-budget audit

[khempenius]

Adds audit only; does not add it to default config or add renderer code. That will be done in a later PR.

This audit returns details in the following format:

{
  metric: 'first-contentful-paint',
  label: 'First Contentful Paint',
  measurement: 1256.3333,
  overBudget: 562.53444
}

Background info on timing budgets implementation:
The performance-budget audit is becoming resource-budget audit; timing budgets are being added as a a separate timing-budget audit. Both audits are part of the budgets group.

Issue: #8917

[patrickhulce]

lookin' good!

Probably should have brought this up earlier, but have we given thought to what's going to happen with our first non-timing metrics like CLS when they land? Will they be covered by budgets.timing and this audit? Will we need a new audit? Will we go through another audit id rejiggering? May not need to decide right now, but it'd be nice to avoid a breaking budgets change every major if we can plan ahead :)

[khempenius]

@patrickhulce

I think something like CLS should be covered by a separate section in budget.json. The exact name would need more thought, but it could be something like budget.layout or budget.metrics, etc. & the section would have its own corresponding audit. This would not entail any breaking changes or audit id renames.

I also think you might also be able to make the argument that something like CLS should be enforced via lighthouse-ci rather than budget.json.

[patrickhulce]

LGTM! excited for the surfacing phase :D

[patrickhulce]

@exterkamp should we be keeping in mind any particular timeline for tc roundrip of strings that we need to release in time? I guess we're only targeting an alpha for CDS but having all the metrics disappear for example would be bummer

[brendankenny]

oh, thanks for pulling in that TimingSummary fix, too!

LGTM