name: histograms description: Manage Chromium histograms and enums metadata. Use this skill when adding code that logs a histogram or when updating metadata in histograms.xml or enums.xml.

Histograms

This skill provides guidance and workflows for logging histograms and managing their metadata in the Chromium codebase.

Overview

When adding code that logs a histogram, you must also add metadata about that histogram and any associated enums to ensure they are properly tracked and interpreted.

Guidelines

Metadata Files

  • Histograms: Metadata goes in histograms.xml.
  • Enums: Metadata about enums goes in enums.xml in the same directory as the corresponding histograms.xml.

Directory Structure

Metadata files are located in subdirectories of //tools/metrics/histograms/metadata/. The subdirectory name is based on the first part of the histogram name (e.g., Platform.Foo would likely be in metadata/platform/). If the correct subdirectory is unclear, ask the user.

Ownership

Histograms must have at least two owners:

  1. The user who requested the change (usually the primary owner).
  2. A relevant team (if possible). If you're unsure who to list as the second owner, ask the user.

Expiry Date

Set the expiry date to 3 months in the future from the date you add the histogram, unless a specific date is more appropriate.

Workflow

  1. Identify the Histogram: Determine the name of the histogram being logged or updated.
  2. Locate Metadata Directory: Find the appropriate subdirectory in //tools/metrics/histograms/metadata/.
  3. Update histograms.xml: Add or update the <histogram> entry.
  4. Update enums.xml (if applicable): If the histogram uses an enum, ensure the corresponding <enum> and its <int> values are defined in enums.xml.
  5. Verify: Check //tools/metrics/histograms/README.md for additional policies.