Metrics - Add actions/README.md

base/metrics/user_metrics.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_METRICS_USER_METRICS_H_
 #define BASE_METRICS_USER_METRICS_H_
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/metrics/user_metrics_action.h"
 #include "base/single_thread_task_runner.h"
 
 namespace base {
 
 // This module provides some helper functions for logging actions tracked by
 // the user metrics system.
 
+// For best practices on deciding when to emit a user action, see
+// https://chromium.googlesource.com/chromium/src.git/+/HEAD/tools/metrics/actions/README.md
+
 // Record that the user performed an action.
 // This function must be called after the task runner has been set with
 // SetRecordActionTaskRunner().
 //
 // "Action" here means a user-generated event:
 //   good: "Reload", "CloseTab", and "IMEInvoked"
 //   not good: "SSLDialogShown", "PageLoaded", "DiskFull"
 // We use this to gather anonymized information about how users are
 // interacting with the browser.
 // WARNING: In calls to this function, UserMetricsAction should be followed by a
@@ skipping 31 matching lines @@
 BASE_EXPORT void AddActionCallback(const ActionCallback& callback);
 BASE_EXPORT void RemoveActionCallback(const ActionCallback& callback);
 
 // Set the task runner on which to record actions.
 BASE_EXPORT void SetRecordActionTaskRunner(
     scoped_refptr<SingleThreadTaskRunner> task_runner);
 
 }  // namespace base
 
 #endif  // BASE_METRICS_USER_METRICS_H_