Log operator code histogram on new metric log

chrome/browser/metrics/metrics_service.h

Index: chrome/browser/metrics/metrics_service.h
diff --git a/chrome/browser/metrics/metrics_service.h b/chrome/browser/metrics/metrics_service.h
index 1499ddf9528af66c8d55f7b588e22e02402f31a3..a54b69b71d692570afd658beabdc7c1f05e630de 100644
--- a/chrome/browser/metrics/metrics_service.h
+++ b/chrome/browser/metrics/metrics_service.h
@@ -18,6 +18,7 @@
 #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/time/time.h"
 #include "chrome/browser/metrics/metrics_log.h"
@@ -36,6 +37,7 @@
 #include "chrome/browser/chromeos/external_metrics.h"
 #endif
 
+class ChromeBrowserMetricsLogObserver;
 class MetricsReportingScheduler;
 class PrefService;
 class PrefRegistrySimple;
@@ -108,6 +110,19 @@ struct SyntheticTrialGroup {
   SyntheticTrialGroup(uint32 trial, uint32 group);
 };
 
+class MetricsLogObserver {

[Ilya Sherman, 2014/05/07 01:03:16]

nit: I think "MetricsServiceObserver" is more accurate, given where this class
is defined.  Also, could you please extract this class out to its own header
file?

[bolian, 2014/05/07 02:20:26]

Done.

+ public:
+  // Will be called when a new MetricsLog is created.
+  virtual void OnNewMetricsLog() = 0;

[Ilya Sherman, 2014/05/07 01:03:16]

nit: "OnDidCreateMetricsLog()" or something else involving a verb :)

[bolian, 2014/05/07 02:20:26]

Done.

+
+ protected:
+  MetricsLogObserver() {}
+  virtual ~MetricsLogObserver() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MetricsLogObserver);
+};
+
 class MetricsService
     : public chrome_browser_metrics::TrackingSynchronizerObserver,
       public content::BrowserChildProcessObserver,
@@ -361,6 +376,11 @@ class MetricsService
   // Set up client ID, session ID, etc.
   void InitializeMetricsState();
 
+  // Registers/Unregsiters |observer| to receive MetricsLog notifications.

[Ilya Sherman, 2014/05/07 01:03:16]

nit: "Un" -> "un"

[bolian, 2014/05/07 02:20:26]

Done.

+  void AddMetricsLogObserver(MetricsLogObserver* observer);
+  void RemoveMetricsLogObserver(MetricsLogObserver* observer);
+  void NotifyOnNewMetricsLog();
+
   // Schedule the next save of LocalState information.  This is called
   // automatically by the task that performs each save to schedule the next one.
   void ScheduleNextStateSave();
@@ -582,21 +602,28 @@ class MetricsService
   // Field trial groups that map to Chrome configuration states.
   SyntheticTrialGroups synthetic_trial_groups_;
 
+  // Observers of MetricsLog.
+  ObserverList<MetricsLogObserver> metrics_log_observers_;
+
+  friend class MetricsServiceHelper;
+
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, IsPluginProcess);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest,
                            PermutedEntropyCacheClearedWhenLowEntropyReset);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, RegisterSyntheticTrial);
+  FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, MetricsLogObserver);
 
   DISALLOW_COPY_AND_ASSIGN(MetricsService);
 };
 
-// This class limits and documents access to the IsMetricsReportingEnabled() and
-// IsCrashReportingEnabled() methods. Since these methods are private, each user
-// has to be explicitly declared as a 'friend' below.
+// This class limits and documents access to metrics service helper methods.
+// Since these methods are private, each user has to be explicitly declared
+// as a 'friend' below.
 class MetricsServiceHelper {
  private:
   friend bool prerender::IsOmniboxEnabled(Profile* profile);
   friend class ChromeRenderMessageFilter;
+  friend class ::ChromeBrowserMetricsLogObserver;

[Ilya Sherman, 2014/05/07 01:03:16]

nit: Alphabetically, this should come before line 625 (though the namespaces
make it weird).

[bolian, 2014/05/07 02:20:26]

Done.

   friend class ::CrashesDOMHandler;
   friend class extensions::ExtensionDownloader;
   friend class extensions::ManifestFetchData;
@@ -617,6 +644,11 @@ class MetricsServiceHelper {
   // IsMetricsReportingEnabled for desktop Chrome.
   static bool IsCrashReportingEnabled();
 
+  // Registers/Unregsiters |observer| to receive MetricsLog notifications
+  // from metric service.
+  static void AddMetricsLogObserver(MetricsLogObserver* observer);
+  static void RemoveMetricsLogObserver(MetricsLogObserver* observer);
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(MetricsServiceHelper);
 };