Adding synthetic field trial for DataReductionProxyEnabled

chrome/browser/metrics/metrics_service_accessor.h

Index: chrome/browser/metrics/metrics_service_accessor.h
diff --git a/chrome/browser/metrics/metrics_service_accessor.h b/chrome/browser/metrics/metrics_service_accessor.h
index 26ce88e7dee4818947d263edf76809fc339dd0f5..255ace8de23475caaf9c51d6fa38847bf2245ef1 100644
--- a/chrome/browser/metrics/metrics_service_accessor.h
+++ b/chrome/browser/metrics/metrics_service_accessor.h
@@ -5,8 +5,11 @@
 #ifndef CHROME_BROWSER_METRICS_METRICS_SERVICE_ACCESSOR_H_
 #define CHROME_BROWSER_METRICS_METRICS_SERVICE_ACCESSOR_H_
 
+#include <string>
+
 #include "base/macros.h"
 
+class MetricsService;
 class MetricsServiceObserver;
 
 // This class limits and documents access to metrics service helper methods.
@@ -23,6 +26,17 @@ class MetricsServiceAccessor {
   static void AddMetricsServiceObserver(MetricsServiceObserver* observer);
   static void RemoveMetricsServiceObserver(MetricsServiceObserver* observer);
 
+  // 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.
+  static bool RegisterSyntheticFieldTrial(MetricsService* metrics_service,
+                                          const std::string& trial,
+                                          const std::string& group);
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MetricsServiceAccessor);
 };