Adding synthetic field trial for DataReductionProxyEnabled

chrome/browser/metrics/chrome_metrics_service_accessor.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 CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_ACCESSOR_H_
 #define CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_ACCESSOR_H_
 
 #include "base/gtest_prod_util.h"
 #include "base/macros.h"
 #include "chrome/browser/metrics/metrics_service_accessor.h"
@@ skipping 22 matching lines @@
 
 // This class limits and documents access to metrics service helper methods.
 // Since these methods are private, each user has to be explicitly declared
 // as a 'friend' below.
 class ChromeMetricsServiceAccessor : public MetricsServiceAccessor {
  private:
   friend bool prerender::IsOmniboxEnabled(Profile* profile);
   friend class ::ChromeBrowserMetricsServiceObserver;
   friend class ChromeRenderMessageFilter;
   friend class ::CrashesDOMHandler;
+  friend class DataReductionProxyChromeSettings;
   friend class extensions::ExtensionDownloader;
   friend class extensions::ManifestFetchData;
   friend class extensions::MetricsPrivateGetIsCrashReportingEnabledFunction;
   friend class ::FlashDOMHandler;
   friend class system_logs::ChromeInternalLogSource;
 
   FRIEND_TEST_ALL_PREFIXES(ChromeMetricsServiceAccessorTest,
                            MetricsReportingEnabled);
   FRIEND_TEST_ALL_PREFIXES(ChromeMetricsServiceAccessorTest,
                            CrashReportingEnabled);
 
   // Returns true if prefs::kMetricsReportingEnabled is set.
   // TODO(asvitkine): Consolidate the method in MetricsStateManager.
   // TODO(asvitkine): This function does not report the correct value on
   // Android and ChromeOS, see http://crbug.com/362192.
   static bool IsMetricsReportingEnabled();
 
   // Returns true if crash reporting is enabled.  This is set at the platform
   // level for Android and ChromeOS, and otherwise is the same as
   // 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);
 };
 
 #endif  // CHROME_BROWSER_METRICS_CHROME_METRICS_SERVICE_ACCESSOR_H_