This adds a weather feature to quick suggest. It periodically fetches a weather
suggestion from Merino. UrlbarProviderQuickSuggest shows the suggestion when the
search string is empty ("zero prefix").
The implementation of the UrlbarResult returned by UrlbarProviderQuickSuggest is
only temporary. Mandy is working on the final UI in
[SNT-323](https://mozilla-hub.atlassian.net/browse/SNT-323). Landing a temporary
implementation allows Mandy to base her patch on it and trigger real weather
suggestions from Merino to test her implementation against. It also lets people
on the team test weather suggestions without having to wait for the final UI to
land.
I added the following prefs and Nimbus variable to control the feature. It will
initially be rolled out in an experiment, so we need a Nimbus variable. In the
initial experiment, users will be able to dismiss the suggestion but not toggle
a checkbox in about:preferences.
* `weatherFeatureGate` - Nimbus variable that controls the whole feature
* `browser.urlbar.weather.featureGate` - Fallback pref for the Nimbus variable
* `browser.urlbar.suggest.weather` - When the feature gate pref is true, this
determines whether the suggestion should be shown. In a future patch, we'll
flip this to false when users dismiss the suggestion.
I set the fetch interval to 30 minutes. That seems reasonable considering that
the suggestion contains the current temperature and weather. Merino will set
caching headers appropriately so that Firefox won't actually make a new network
request if the previously fetched suggestion is new enough.
Depends on D161368
Differential Revision: https://phabricator.services.mozilla.com/D161410
26a76fee34