Adding synthetic field trial for DataReductionProxyEnabled

components/metrics/metrics_service.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.
 
 // This file defines a service that collects information about the user
 // experience in order to help improve future versions of the app.
 
 #ifndef COMPONENTS_METRICS_METRICS_SERVICE_H_
 #define COMPONENTS_METRICS_METRICS_SERVICE_H_
 
@@ skipping 49 matching lines @@
 // Chrome configuration state. For example, the trial name could map to
 // a preference name, and the group name could map to a preference value.
 struct SyntheticTrialGroup {
  public:
   ~SyntheticTrialGroup();
 
   variations::ActiveGroupId id;
   base::TimeTicks start_time;
 
  private:
+  //Synthetic field trial users:
   friend class MetricsService;
+  friend class DataReductionProxyChromeSettings;

[Alexei Svitkine (slow), 2014/07/30 17:27:04]

This is a layering violation, since the component shouldn't know anything about
things outside of the component.

Instead, please add the friend declaration to ChromeMetricsServiceAccessor in
chrome/browser/metrics and add a method on the accessor to register a synthetic
trial (the method can actually just be a static that takes two strings and
inside it, it could do the whole block that uses
g_browser_process->metrics_service() and passes the SyntheticTrial object.

[megjablon, 2014/07/30 18:50:48]

Done.

   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, RegisterSyntheticTrial);
 
   // This constructor is private specifically so as to control which code is
   // able to access it. New code that wishes to use it should be added as a
   // friend class.
   SyntheticTrialGroup(uint32 trial, uint32 group);
 };
 
 class MetricsService : public base::HistogramFlattener {
  public:
@@ skipping 381 matching lines @@
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, IsPluginProcess);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, MetricsServiceObserver);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest,
                            PermutedEntropyCacheClearedWhenLowEntropyReset);
   FRIEND_TEST_ALL_PREFIXES(MetricsServiceTest, RegisterSyntheticTrial);
 
   DISALLOW_COPY_AND_ASSIGN(MetricsService);
 };
 
 #endif  // COMPONENTS_METRICS_METRICS_SERVICE_H_