Add a histogram to measure number of synthetic UMA trials.

components/metrics/metrics_service.h

Index: components/metrics/metrics_service.h
diff --git a/components/metrics/metrics_service.h b/components/metrics/metrics_service.h
index a6259537792409b2244c00cfd1d6adf6139024c1..fab569833d8118894604a92caa8be3d0aa1f4d13 100644
--- a/components/metrics/metrics_service.h
+++ b/components/metrics/metrics_service.h
@@ -364,6 +364,9 @@ class MetricsService : public base::HistogramFlattener {
   // Creates a new MetricsLog instance with the given |log_type|.
   scoped_ptr<MetricsLog> CreateLog(MetricsLog::LogType log_type);
 
+  // Records the current environment (system profile) in |log|.
+  void RecordCurrentEnvironment(MetricsLog* log);
+
   // Record complete list of histograms into the current log.
   // Called when we close a log.
   void RecordCurrentHistograms();