Split UserMetrics into API vs. implementation. Move API to content/public.

content/public/browser/user_metrics.h

+// Copyright (c) 2011 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 CONTENT_PUBLIC_BROWSER_USER_METRICS_H_
+#define CONTENT_PUBLIC_BROWSER_USER_METRICS_H_
+#pragma once
+
+#include <string>
+
+#include "content/common/content_export.h"
+
+namespace content {
+
+// This module provides some helper functions for logging actions tracked by
+// the user metrics system.
+
+
+// UserMetricsAction exist purely to standardize on the paramters passed to
+// UserMetrics. That way, our toolset can scan the sourcecode reliable for
+// constructors and extract the associated string constants
+struct UserMetricsAction {
+  const char* str_;
+  explicit UserMetricsAction(const char* str) : str_(str) {}
+};
+
+// Record that the user performed an action.
+// "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 and a
+// string literal parameter must be on the same line, e.g.
+//   content::RecordAction(
+//       content::UserMetricsAction("my extremely long action name"));
+// because otherwise our processing scripts won't pick up on new actions.
+//
+// Once a new recorded action is added, run chrome/tools/extract_actions.py
+// to generate a new mapping of [action hashes -> metric names] and send it
+// out for review to be updated.
+//
+// For more complicated situations (like when there are many different
+// possible actions), see RecordComputedAction.
+CONTENT_EXPORT void RecordAction(const UserMetricsAction& action);
+
+// This function has identical input and behavior to RecordAction, but is
+// not automatically found by the action-processing scripts.  It can be used
+// when it's a pain to enumerate all possible actions, but if you use this
+// you need to also update the rules for extracting known actions in
+// chrome/tools/extract_actions.py.
+CONTENT_EXPORT void RecordComputedAction(const std::string& action);
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_USER_METRICS_H_