Chromium Feature Toggles: Switches, Flags, and Blink Runtime

The provided text offers a comprehensive technical overview of the four primary mechanisms utilized in Chromium for toggling features and behaviors at runtime. It distinguishes between command-line switches (low-level, developer-focused tokens), base::Feature flags (the preferred modern system integrated with experimentation via Finch and metrics), Blink’s RuntimeEnabledFeatures (required for gating web-exposed functionality and managed through a JSON configuration), and Chrome Flags (chrome://flags), which serve as a persistent, user-friendly UI layer over the underlying switches and features. Crucially, the sources explain the layered hierarchy of control, noting that user-defined switches and flags typically override server-side experimentation settings, and they provide best practices for contributors, especially concerning the lifecycle of a feature from development behind a flag to eventual flag removal upon stable shipment.