For #15366: Add recently closed tabs metrics.

[mcarare]

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

To download an APK when reviewing a PR:

1. click on Show All Checks,
2. click Details next to "Taskcluster (pull_request)" after it appears and then finishes with a green checkmark,
3. click on the "Fenix - assemble" task, then click "Run Artifacts".
4. the APK links should be on the left side of the screen, named for each CPU architecture

[codecov-io]

Codecov Report

Merging #16739 (dcafd20) into master (4b56aeb) will decrease coverage by 0.03%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master   #16739      +/-   ##
============================================
- Coverage     30.14%   30.10%   -0.04%     
  Complexity     1206     1206              
============================================
  Files           454      454              
  Lines         18556    18597      +41     
  Branches       2560     2565       +5     
============================================
+ Hits           5594     5599       +5     
- Misses        12520    12556      +36     
  Partials        442      442              

Impacted Files	Coverage Δ	Complexity Δ
...java/org/mozilla/fenix/components/metrics/Event.kt	33.88% <0.00%> (-0.12%)	0.00 <0.00> (ø)
...la/fenix/components/metrics/GleanMetricsService.kt	12.45% <0.00%> (-0.03%)	5.00 <0.00> (ø)
...ava/org/mozilla/fenix/tabtray/TabTrayController.kt	73.91% <0.00%> (-1.09%)	0.00 <0.00> (ø)
...a/org/mozilla/gecko/search/SearchWidgetProvider.kt	24.00% <0.00%> (-11.14%)	1.00% <0.00%> (ø%)

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[mcarare]

Request for data collection review form

All questions are mandatory. You must receive review from a data steward peer on your responses to these questions before shipping new data collection.

1) What questions will you answer with this data?
How often users access the recently closed tabs list.

2) Why does Mozilla need to answer these questions? Are there benefits for users? Do we need this information to address product or business requirements?
Measure whether this feature is used by users and how often.

3) What alternative methods did you consider to answer these questions? Why were they not sufficient?
This is the only way.

4) Can current instrumentation answer these questions?
No. We need a new specific event for a specific app feature.

5) List all proposed measurements and indicate the category of data collection for each measurement, using the Firefox data collection categories found on the Mozilla wiki.

Note that the data steward reviewing your request will characterize your data collection based on the highest (and most sensitive) category.

Measurement Description	Data Collection Category	Tracking Bug #
Accessed recently closed tabs list	Category 2	https://github.com//issues/15366

6) Please provide a link to the documentation for this data collection which describes the ultimate data set in a public, complete, and accurate way.
This collection is documented in the metrics.md document document included in the project - https://github.com/mozilla-mobile/fenix/blob/master/docs/metrics.md

7) How long will this data be collected? Choose one of the following:
Until 2021-05-10.

8) What populations will you measure?
All release channels and locales.

9) If this data collection is default on, what is the opt-out mechanism for users?
Users can opt of of data collection by disabling Usage and technical data from Settings -> Data collection.

10) Please provide a general description of how you will analyze this data.
Glean / Amplitude

11) Where do you intend to share the results of your analysis?
Only on Glean, Amplitude and with mobile teams.

12) Is there a third-party tool (i.e. not Telemetry) that you are proposing to use for this data collection?
No.

[boek]

Data Review Form (to be filled by Data Stewards)

1. Is there or will there be documentation that describes the schema for the ultimate data set in a public, complete, and accurate way?
   Yes, metrics.yaml and metrics.md

2. Is there a control mechanism that allows the user to turn the data collection on and off?
   Yes, Fenix data collection settings.

3. If the request is for permanent data collection, is there someone who will monitor the data over time?
   No, Fenix team will monitor

4. Using the category system of data types on the Mozilla wiki, what collection type of data do the requested measurements fall under?
   Type 2

5. Is the data collection request for default-on or default-off?
   Default on

6. Does the instrumentation include the addition of any new identifiers (whether anonymous or otherwise; e.g., username, random IDs, etc. See the appendix for more details)?
   No

7. Is the data collection covered by the existing Firefox privacy notice?
   Yes

8. Does there need to be a check-in in the future to determine whether to renew the data?
   Has expiry

9. Does the data collection use a third-party collection tool?
   No