[ads] RichNTT: Desktop

[tmancey]

Resolves brave/brave-browser#43512

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 spec.

[github-actions]

Chromium major version is behind target branch (132.0.6834.83 vs 133.0.6943.27). Please rebase.

[github-actions]

[puLL-Merge] - brave/brave-core@27358

Here's my review of the PR:

Description

This PR adds support for rich media ads in the New Tab Page (NTP) background. It includes the ability to serve rich media content through an untrusted WebUI frame, handle new media playback events (50% and 75%), and support interaction events. The changes also refactor how new tab page ads are managed, moving away from catalog-based ads to component-based ads.

Possible Issues

1. The PR modifies path traversal checks and security headers for untrusted content - this needs thorough testing to ensure the sandboxing is effective
2. Some unit tests were removed or disabled which could reduce test coverage
3. The changes introduce runtime parsing of dynamic content which could impact performance

Security Hotspots

1. URL Validation: The MaybeGetFilePathForRequestPath method needs to ensure no path traversal is possible when serving rich media content
2. CSP Headers: The new Content Security Policy settings for rich media frames need to be restrictive enough to prevent malicious behavior
3. Message Passing: The untrusted frame communication via postMessage needs proper origin validation

Changes

Changes

1. ntp_sponsored_rich_media_source.h/cc:

• Added new source handler for rich media content
• Implements strict CSP and sandboxing
• Handles path validation and file serving

2. ntp_p3a_helper_impl.cc:

• Added support for new event types (interaction, media_50, media_75)
• Updated metrics reporting

3. view_counter_service.cc:

• Added support for rich media ad events
• Modified wallpaper handling to support rich media type

4. UI Components:

• Added new iframe component for rich media content
• Updated event handling for media playback tracking
• Added support for interaction events

sequenceDiagram
    participant Browser
    participant NTPService
    participant RichMediaSource
    participant AdService
    
    Browser->>NTPService: Request new tab page
    NTPService->>RichMediaSource: Init rich media frame
    RichMediaSource->>RichMediaSource: Validate paths & set CSP
    RichMediaSource-->>NTPService: Return sandboxed frame
    NTPService-->>Browser: Display rich media content
    
    Browser->>AdService: Report media events
    AdService->>AdService: Process events (25%,50%,75%,100%)
    AdService-->>Browser: Update metrics

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[tmancey]

Closing and will reopen a new PR.