Use a different algorithm with the low entropy source for field trials.

chrome/browser/metrics/metrics_service.h

 // Copyright (c) 2012 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 CHROME_BROWSER_METRICS_METRICS_SERVICE_H_
 #define CHROME_BROWSER_METRICS_METRICS_SERVICE_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
+#include "base/metrics/field_trial.h"
 #include "base/process_util.h"
 #include "chrome/browser/metrics/metrics_log.h"
 #include "chrome/browser/metrics/tracking_synchronizer_observer.h"
 #include "chrome/common/metrics/metrics_service_base.h"
 #include "chrome/installer/util/google_update_settings.h"
 #include "content/public/browser/notification_observer.h"
 #include "content/public/browser/notification_registrar.h"
 #include "net/url_request/url_fetcher_delegate.h"
 
 #if defined(OS_CHROMEOS)
 #include "chrome/browser/chromeos/external_metrics.h"
 #endif
 
 class BookmarkModel;
 class BookmarkNode;
 class MetricsReportingScheduler;
 class PrefService;
 class Profile;
 class TemplateURLService;
 
 namespace base {
 class DictionaryValue;
+class EntropyProvider;

[Ilya Sherman, 2012/08/17 07:34:28]

Isn't this class defined as a subtype of the FieldTrial class?

[Alexei Svitkine (slow), 2012/08/17 14:08:59]

You're right. This got left over from a previous iteration where I had the
EntropyProvider as a standalone interface. Removed.

 class MessageLoopProxy;
 }
 
 namespace content {
 class RenderProcessHost;
 }
 
 namespace extensions {
 class ExtensionDownloader;
 }
@@ skipping 28 matching lines @@
   // StartRecordingOnly starts the metrics recording but not reporting, for use
   // in tests only.
   void Start();
   void StartRecordingOnly();
   void Stop();
 
   // Returns the client ID for this client, or the empty string if metrics
   // recording is not currently running.
   std::string GetClientId();
 
-  // Returns the preferred entropy source used to seed persistent activities
+  // Returns the preferred entropy provider used to seed persistent activities
   // based on whether or not metrics reporting will permitted on this client.
   // The caller must determine if metrics reporting will be enabled for this
-  // client and pass that state in as |reporting_will_be_enabled|. If
-  // |reporting_will_be_enabled| is true, this method returns the client ID
-  // concatenated with the low entropy source. Otherwise, this method just
-  // returns the low entropy source. Note that this reporting state can not be
-  // checked by reporting_active() because this method may need to be called
-  // before the MetricsService needs to be started.
-  std::string GetEntropySource(bool reporting_will_be_enabled);
+  // client and pass that state in as |reporting_will_be_enabled|.
+  //
+  // If |reporting_will_be_enabled| is true, this method returns an entropy
+  // provider that has a high source of entropy, partially based on the client
+  // ID. Otherwise, an entropy provider that is based on a low entropy source
+  // is returned.
+  //
+  // Note that this reporting state can not be checked by reporting_active()
+  // because this method may need to be called before the MetricsService needs
+  // to be started.
+  base::FieldTrial::EntropyProvider* GetEntropyProvider(
+      bool reporting_will_be_enabled);
 
   // Force the client ID to be generated. This is useful in case it's needed
   // before recording.
   void ForceClientIdCreation();
 
   // At startup, prefs needs to be called with a list of all the pref names and
   // types we'll be using.
   static void RegisterPrefs(PrefService* local_state);
 
   // Set up notifications which indicate that a user is performing work. This is
@@ skipping 398 matching lines @@
   friend bool prerender::IsOmniboxEnabled(Profile* profile);
   friend class extensions::ExtensionDownloader;
 
   // Returns true if prefs::kMetricsReportingEnabled is set.
   static bool IsMetricsReportingEnabled();
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(MetricsServiceHelper);
 };
 
 #endif  // CHROME_BROWSER_METRICS_METRICS_SERVICE_H_