Introduce a MetricsDataProvider interface.

chrome/browser/metrics/metrics_service.h

 // Copyright (c) 2012 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.
 
 // This file defines a service that collects information about the user
 // experience in order to help improve future versions of the app.
 
 #ifndef CHROME_BROWSER_METRICS_METRICS_SERVICE_H_
 #define CHROME_BROWSER_METRICS_METRICS_SERVICE_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
 #include "base/memory/weak_ptr.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/user_metrics.h"
 #include "base/observer_list.h"
 #include "base/process/kill.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "chrome/browser/metrics/metrics_log.h"
 #include "chrome/browser/metrics/metrics_service_observer.h"
 #include "chrome/browser/metrics/tracking_synchronizer_observer.h"
 #include "chrome/common/metrics/metrics_service_base.h"
 #include "chrome/installer/util/google_update_settings.h"
+#include "components/metrics/metrics_data_provider.h"

[Ilya Sherman, 2014/05/19 14:45:00]

nit: Can this be forward-declared?

[Alexei Svitkine (slow), 2014/05/19 15:23:02]

Doesn't look like it:

../../base/stl_util.h:44:5: error: deleting pointer to incomplete type
'metrics::MetricsDataProvider' may cause undefined behavior
[-Werror,-Wdelete-incomplete]
    delete *temp;
    ^      ~~~~~
../../base/stl_util.h:140:3: note: in instantiation of function template
specialization
'STLDeleteContainerPointers<__gnu_cxx::__normal_iterator<metrics::MetricsDataProvider
**, std::vector<metrics::MetricsDataProvider *,
std::allocator<metrics::MetricsDataProvider *> > > >' requested here
  STLDeleteContainerPointers(container->begin(), container->end());
  ^
../../base/memory/scoped_vector.h:97:18: note: in instantiation of function
template specialization
'STLDeleteElements<std::vector<metrics::MetricsDataProvider *,
std::allocator<metrics::MetricsDataProvider *> > >' requested here
  void clear() { STLDeleteElements(&v_); }
                 ^
../../base/memory/scoped_vector.h:37:21: note: in instantiation of member
function 'ScopedVector<metrics::MetricsDataProvider>::clear' requested here
  ~ScopedVector() { clear(); }

 #include "content/public/browser/browser_child_process_observer.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "content/public/browser/user_metrics.h"
 #include "net/url_request/url_fetcher_delegate.h"
 
 #if defined(OS_ANDROID)
 #include "chrome/browser/android/activity_type_ids.h"
 #elif defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/external_metrics.h"
@@ skipping 235 matching lines @@
   // Registers a field trial name and group to be used to annotate a UMA report
   // with a particular Chrome configuration state. A UMA report will be
   // annotated with this trial group if and only if all events in the report
   // were created after the trial is registered. Only one group name may be
   // registered at a time for a given trial_name. Only the last group name that
   // is registered for a given trial name will be recorded. The values passed
   // in must not correspond to any real field trial in the code.
   // To use this method, SyntheticTrialGroup should friend your class.
   void RegisterSyntheticFieldTrial(const SyntheticTrialGroup& trial_group);
 
+  // Register the specified |provider| to provide additional metrics into the
+  // UMA log. Should be called during MetricsService initialization only.
+  void RegisterDataProvider(scoped_ptr<metrics::MetricsDataProvider> provider);
+
   // Check if this install was cloned or imaged from another machine. If a
   // clone is detected, reset the client id and low entropy source. This
   // should not be called more than once.
   void CheckForClonedInstall();
 
  private:
   // The MetricsService has a lifecycle that is stored as a state.
   // See metrics_service.cc for description of this lifecycle.
   enum State {
     INITIALIZED,                    // Constructor was called.
@@ skipping 185 matching lines @@
 
   // Returns a list of synthetic field trials that were active for the entire
   // duration of the current log.
   void GetCurrentSyntheticFieldTrials(
       std::vector<chrome_variations::ActiveGroupId>* synthetic_trials);
 
   // Used to manage various metrics reporting state prefs, such as client id,
   // low entropy source and whether metrics reporting is enabled. Weak pointer.
   metrics::MetricsStateManager* state_manager_;
 
+  // Additional metrics data providers that have been registered.

[Ilya Sherman, 2014/05/19 14:45:00]

nit: Additional over what?  I'd probably just omit the word, and write this as
"Registered metrics data providers."

[Alexei Svitkine (slow), 2014/05/19 15:23:02]

Done.

+  ScopedVector<metrics::MetricsDataProvider> data_providers_;
+
   base::ActionCallback action_callback_;
 
   content::NotificationRegistrar registrar_;
 
   // Set to true when |ResetMetricsIDsIfNecessary| is called for the first time.
   // This prevents multiple resets within the same Chrome session.
   bool metrics_ids_reset_check_performed_;
 
   // Indicate whether recording and reporting are currently happening.
   // These should not be set directly, but by calling SetRecording and
@@ skipping 140 matching lines @@
 
   // Registers/unregisters |observer| to receive MetricsLog notifications
   // from metrics service.
   static void AddMetricsServiceObserver(MetricsServiceObserver* observer);
   static void RemoveMetricsServiceObserver(MetricsServiceObserver* observer);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(MetricsServiceHelper);
 };
 
 #endif  // CHROME_BROWSER_METRICS_METRICS_SERVICE_H_