Adding synthetic field trial for DataReductionProxyEnabled

chrome/browser/metrics/chrome_metrics_service_accessor.h

Index: chrome/browser/metrics/chrome_metrics_service_accessor.h
diff --git a/chrome/browser/metrics/chrome_metrics_service_accessor.h b/chrome/browser/metrics/chrome_metrics_service_accessor.h
index a891f27c5e62918a717675e74c2cd1b2d170903c..e62cc4ec35e8df737b76fb75add09b4074ebb06d 100644
--- a/chrome/browser/metrics/chrome_metrics_service_accessor.h
+++ b/chrome/browser/metrics/chrome_metrics_service_accessor.h
@@ -40,6 +40,7 @@ class ChromeMetricsServiceAccessor : public MetricsServiceAccessor {
   friend class ::ChromeBrowserMetricsServiceObserver;
   friend class ChromeRenderMessageFilter;
   friend class ::CrashesDOMHandler;
+  friend class DataReductionProxyChromeSettings;
   friend class extensions::ExtensionDownloader;
   friend class extensions::ManifestFetchData;
   friend class extensions::MetricsPrivateGetIsCrashReportingEnabledFunction;
@@ -62,6 +63,16 @@ class ChromeMetricsServiceAccessor : public MetricsServiceAccessor {
   // IsMetricsReportingEnabled for desktop Chrome.
   static bool IsCrashReportingEnabled();
 
+  // 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(const std::string& trial,
+                                        const std::string& group);
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(ChromeMetricsServiceAccessor);
 };