chromium/components/page_load_metrics/browser/observers/use_counter/ukm_features.cc

// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "base/no_destructor.h"
#include "components/page_load_metrics/browser/observers/use_counter_page_load_metrics_observer.h"

// This file defines a list of UseCounter WebFeature measured in the
// UKM-based UseCounter. Features must all satisfy UKM privacy requirements
// (see go/ukm). In addition, features should only be added if it's shown to be
// (or highly likely to be) rare, e.g. <1% of page views as measured by UMA.
//
// UKM-based UseCounter should be used to cover the case when UMA UseCounter
// data shows a behaviour that is rare but too common to blindly change.
// UKM-based UseCounter would allow us to find specific pages to reason about
// whether a breaking change is acceptable or not.
//
// This event is emitted for every page load and is not sub-sampled by the UKM
// system. The WebFeature::kPageVisits is always present in the event, so
// it is valid to take the ratio of events with your feature to kPageVisit to
// estimate "percentage of page views using a feature". Note that the lack of
// sub-sampling is the reason why this event must only be used for rare
// features.
//
// Obsolete UseCounters (kOBSOLETE_*) should be removed from this list.

WebFeature;

// UKM-based UseCounter features (WebFeature) should be defined in
// opt_in_features list.
const UseCounterMetricsRecorder::UkmFeatureList&
UseCounterMetricsRecorder::GetAllowedUkmFeatures() { … }