Add a histogram to debug metrics entropy source use.

components/metrics/metrics_state_manager.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 COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_
 #define COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 72 matching lines @@
                            PermutedEntropyCacheClearedWhenLowEntropyReset);
   FRIEND_TEST_ALL_PREFIXES(MetricsStateManagerTest, ResetMetricsIDs);
 
   // Designates which entropy source was returned from this class.
   // This is used for testing to validate that we return the correct source
   // depending on the state of the service.
   enum EntropySourceType {
     ENTROPY_SOURCE_NONE,
     ENTROPY_SOURCE_LOW,
     ENTROPY_SOURCE_HIGH,
+    ENTROPY_SOURCE_ENUM_SIZE,
   };
 
   // Creates the MetricsStateManager with the given |local_state|. Calls
   // |is_reporting_enabled_callback| to query whether metrics reporting is
   // enabled. Clients should instead use Create(), which enforces that a single
   // instance of this class be alive at any given time.
   // |store_client_info| should back up client info to persistent storage such
   // that it is later retrievable by |load_client_info|.
   MetricsStateManager(
       PrefService* local_state,
       const base::Callback<bool(void)>& is_reporting_enabled_callback,
       const StoreClientInfoCallback& store_client_info,
       const LoadClientInfoCallback& load_client_info);
 
   // Backs up the current client info via |store_client_info_|.
   void BackUpCurrentClientInfo();
 
   // Loads the client info via |load_client_info_| and potentially migrates it
   // before returning it if it comes back in its old form.
   scoped_ptr<ClientInfo> LoadClientInfoAndMaybeMigrate();
 
   // Returns the low entropy source for this client. This is a random value
   // that is non-identifying amongst browser clients. This method will
   // generate the entropy source value if it has not been called before.
   int GetLowEntropySource();
 
+  // Updates |entropy_source_returned_| with |type| iff the current value is
+  // ENTROPY_SOURCE_NONE and logs the new value in a histogram.
+  void UpdateEntropySourceReturnedValue(EntropySourceType type);
+
   // Returns the first entropy source that was returned by this service since
   // start up, or NONE if neither was returned yet. This is exposed for testing
   // only.
   EntropySourceType entropy_source_returned() const {
     return entropy_source_returned_;
   }
 
   // Reset the client id and low entropy source if the kMetricsResetMetricIDs
   // pref is true.
   void ResetMetricsIDsIfNecessary();
@@ skipping 27 matching lines @@
   EntropySourceType entropy_source_returned_;
 
   scoped_ptr<ClonedInstallDetector> cloned_install_detector_;
 
   DISALLOW_COPY_AND_ASSIGN(MetricsStateManager);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_