Add a histogram to measure number of synthetic UMA trials.

components/metrics/metrics_service.cc

 // 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.
 
 //------------------------------------------------------------------------------
 // Description of the life cycle of a instance of MetricsService.
 //
 //  OVERVIEW
 //
 // A MetricsService instance is typically created at application startup.  It is
@@ skipping 748 matching lines @@
     log_manager_.DiscardCurrentLog();
     OpenNewLog();  // Start trivial log to hold our histograms.
   }
 
   // Put incremental data (histogram deltas, and realtime stats deltas) at the
   // end of all log transmissions (initial log handles this separately).
   // RecordIncrementalStabilityElements only exists on the derived
   // MetricsLog class.
   MetricsLog* current_log = log_manager_.current_log();
   DCHECK(current_log);
-  std::vector<variations::ActiveGroupId> synthetic_trials;
-  GetCurrentSyntheticFieldTrials(&synthetic_trials);
-  current_log->RecordEnvironment(
-      metrics_providers_.get(), synthetic_trials, GetInstallDate());
+  RecordCurrentEnvironment(current_log);
   base::TimeDelta incremental_uptime;
   base::TimeDelta uptime;
   GetUptimes(local_state_, &incremental_uptime, &uptime);
   current_log->RecordStabilityMetrics(metrics_providers_.get(),
                                       incremental_uptime, uptime);
 
   RecordCurrentHistograms();
   current_log->RecordGeneralMetrics(metrics_providers_.get());
 
   log_manager_.FinishCurrentLog();
@@ skipping 182 matching lines @@
   // Store unsent logs, including the stability log that was just saved, so
   // that they're not lost in case of a crash before upload time.
   log_manager_.PersistUnsentLogs();
 
   has_initial_stability_log_ = true;
 }
 
 void MetricsService::PrepareInitialMetricsLog() {
   DCHECK(state_ == INIT_TASK_DONE || state_ == SENDING_INITIAL_STABILITY_LOG);
 
-  std::vector<variations::ActiveGroupId> synthetic_trials;
-  GetCurrentSyntheticFieldTrials(&synthetic_trials);
-  initial_metrics_log_->RecordEnvironment(metrics_providers_.get(),
-                                          synthetic_trials,
-                                          GetInstallDate());
+  RecordCurrentEnvironment(initial_metrics_log_.get());
   base::TimeDelta incremental_uptime;
   base::TimeDelta uptime;
   GetUptimes(local_state_, &incremental_uptime, &uptime);
 
   // Histograms only get written to the current log, so make the new log current
   // before writing them.
   log_manager_.PauseCurrentLog();
   log_manager_.BeginLoggingWithLog(initial_metrics_log_.Pass());
 
   // Note: Some stability providers may record stability stats via histograms,
@@ skipping 180 matching lines @@
 }
 
 scoped_ptr<MetricsLog> MetricsService::CreateLog(MetricsLog::LogType log_type) {
   return make_scoped_ptr(new MetricsLog(state_manager_->client_id(),
                                         session_id_,
                                         log_type,
                                         client_,
                                         local_state_));
 }
 
+void MetricsService::RecordCurrentEnvironment(MetricsLog* log) {
+  std::vector<variations::ActiveGroupId> synthetic_trials;
+  GetCurrentSyntheticFieldTrials(&synthetic_trials);
+  log->RecordEnvironment(metrics_providers_.get(), synthetic_trials,
+                         GetInstallDate());
+  UMA_HISTOGRAM_COUNTS_100("UMA.SyntheticTrials.Count",
+                           synthetic_trials.size());
+}
+
 void MetricsService::RecordCurrentHistograms() {
   DCHECK(log_manager_.current_log());
   histogram_snapshot_manager_.PrepareDeltas(
       base::Histogram::kNoFlags, base::Histogram::kUmaTargetedHistogramFlag);
 }
 
 void MetricsService::RecordCurrentStabilityHistograms() {
   DCHECK(log_manager_.current_log());
   histogram_snapshot_manager_.PrepareDeltas(
       base::Histogram::kNoFlags, base::Histogram::kUmaStabilityHistogramFlag);
@@ skipping 25 matching lines @@
   local_state_->SetBoolean(path, value);
   RecordCurrentState(local_state_);
 }
 
 void MetricsService::RecordCurrentState(PrefService* pref) {
   pref->SetInt64(metrics::prefs::kStabilityLastTimestampSec,
                  base::Time::Now().ToTimeT());
 }
 
 }  // namespace metrics