Add metric configuration and alternative metric attributes

[DJAndries]

Resolves brave/brave-browser#42541

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

See #20264. Ignore step 1.

[fmarier]

It looks like we always include the refcode now?
In what cases would we omit the refcode before this PR?

[DJAndries]

Previously, we had a small allowlist of a few metrics that included the refcode. In this PR, we only include the refcode is the kRef attribute is provided in the attribute list in the metric config. By default, it's not included.

[iefremov]

why not return a reference?

[DJAndries]

The std::optional<MetricConfig> may not exist i.e. in the case of dynamic metrics, which do not have metric configs in metric_names.h.

[github-actions]

[puLL-Merge] - brave/brave-core@26762

Description

This PR introduces significant changes to the P3A (Privacy-Preserving Product Analytics) system in Brave Core. It adds more granular control over metric configurations, introduces new region and subregion identifiers, and refactors the way metrics are collected and processed.

Possible Issues

1. The changes to metric configurations might require updates to existing metrics or data processing pipelines.
2. The new region and subregion identifiers could potentially impact data analysis if not properly accounted for in downstream processes.

Security Hotspots

1. The addition of more detailed region information (GetRegionIdentifiers) could potentially lead to more precise user identification if not carefully managed.

Changes

Changes

1. components/brave_stats/browser/brave_stats_updater_util.cc/h:

   • Added GetGeneralPlatformIdentifier() function to return a more general platform identifier.

2. components/p3a/metric_config.h:

   • Introduced new MetricConfig structure with various configuration options for metrics.
   • Defined MetricAttribute enum for specifying which attributes to include with metrics.

3. components/p3a/p3a_message.cc/h:

   • Updated GenerateP3AConstellationMessage to use the new MetricConfig.
   • Added support for new attributes like general platform, region, and subregion.

4. components/p3a/message_manager.cc/h:

   • Refactored to use the new MetricConfig for determining metric behavior.
   • Added GetMetricConfig method to retrieve configuration for a given metric.

5. components/p3a/metric_names.h:

   • Updated metric definitions to use the new MetricConfig structure.
   • Removed separate lists for ephemeral, constellation-only, and nebula-only metrics.

6. components/p3a/region.cc/h:

   • Added new files to handle region and subregion identification based on country codes.

7. Various test files:

   • Updated to accommodate the new metric configuration system and region identification.

sequenceDiagram
    participant Client
    participant MessageManager
    participant P3AService
    participant MetricConfig
    participant RegionIdentifier

    Client->>P3AService: Report metric
    P3AService->>MessageManager: Handle metric change
    MessageManager->>MetricConfig: Get metric configuration
    MessageManager->>RegionIdentifier: Get region identifiers
    MessageManager->>MessageManager: Generate constellation message
    MessageManager->>Client: Prepare metric for upload

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[brave-builds]

Released in v1.75.117