For #19915: Add telemetry for the toolbar Home screen button.

[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
  -> No visual changes.
• 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.
  -> No user-facing features.

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[codecov-commenter]

Codecov Report

Merging #19936 (f888015) into master (bd32346) will decrease coverage by 0.00%.
The diff coverage is 25.00%.

@@             Coverage Diff              @@
##             master   #19936      +/-   ##
============================================
- Coverage     36.79%   36.78%   -0.01%     
+ Complexity     1622     1620       -2     
============================================
  Files           535      535              
  Lines         20961    20961              
  Branches       3117     3118       +1     
============================================
- Hits           7712     7710       -2     
- Misses        12356    12358       +2     
  Partials        893      893              

Impacted Files	Coverage Δ
...pp/src/main/java/org/mozilla/fenix/HomeActivity.kt	25.13% <0.00%> (+0.19%)	⬆️
...la/fenix/components/metrics/GleanMetricsService.kt	19.81% <0.00%> (-0.08%)	⬇️
...c/main/java/org/mozilla/fenix/home/HomeFragment.kt	2.42% <ø> (+<0.01%)	⬆️
...ix/home/sessioncontrol/SessionControlController.kt	71.06% <50.00%> (ø)
...java/org/mozilla/fenix/components/metrics/Event.kt	41.32% <100.00%> (+0.16%)	⬆️
...nix/components/toolbar/BrowserToolbarController.kt	91.80% <100.00%> (+0.13%)	⬆️
...java/org/mozilla/fenix/perf/PerformanceInflater.kt	80.00% <0.00%> (-15.00%)	⬇️
...in/java/org/mozilla/fenix/perf/NavGraphProvider.kt	50.00% <0.00%> (-12.50%)	⬇️

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[gabrielluong]

Code looks fine. @mcarare I am wondering if we also filed a DS request to confirm we want this as an event ping, which I think makes sense here, but I guess we should be sure by checking with DS. You may need to ping #data-help on slack.

[mcarare]

Request for data collection review

1. What questions will you answer with this data?
   This data will provide statistics regarding the usage of the new home button on the browser toolbar.

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?
   This will give us an understanding of the usability of the button, info we will use for improving the user experience.

3. What alternative methods did you consider to answer these questions? Why were they not sufficient?
   No alternative is available to answer this question.

4. Can current instrumentation answer these questions?
   No.

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.

Measurement Description	Data Collection Category	Tracking Bug #
Home button clicks	category 2 - Interaction data	#19915

6. How long will this data be collected? Choose one of the following:
   Data will be collected for 6 months initially (ending on 2021-12-10), with the option to renew at that point.


7. What populations will you measure?
   No filters - all locales, channels, etc. Currently, the button is visible only in Nightly.

8. If this data collection is default on, what is the opt-out mechanism for users?
   Default Glean SDK opt-out mechanism.

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

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

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

[tdsmith]

data-review+, thanks!

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, in the probe definition files and the Glean dictionary.

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

Yes, the Firefox telemetry opt-out.

3. If the request is for permanent data collection, is there someone who will monitor the data over time?

n/a

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

Cat 2, interaction data

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 the data collection use a third-party collection tool?

No