Use low entropy for studies that send experiment IDs to Google properties.

components/metrics/metrics_state_manager.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 COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_
 #define COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 43 matching lines @@
 
   // Checks if this install was cloned or imaged from another machine. If a
   // clone is detected, resets the client id and low entropy source. This
   // should not be called more than once.
   void CheckForClonedInstall(
       scoped_refptr<base::SingleThreadTaskRunner> task_runner);
 
   // Returns the preferred entropy provider used to seed persistent activities
   // based on whether or not metrics reporting is permitted on this client.
   //
-  // If metrics reporting is enabled, this method returns an entropy provider
-  // that has a high source of entropy, partially based on the client ID.
-  // Otherwise, it returns an entropy provider that is based on a low entropy
-  // source.
+  // If there's consent to report metrics, this method returns an entropy
+  // provider that has a high source of entropy, partially based on the client
+  // ID. Otherwise, it returns an entropy provider that is based on a low
+  // entropy source.
   std::unique_ptr<const base::FieldTrial::EntropyProvider>
-  CreateEntropyProvider();
+  CreateDefaultEntropyProvider();
+
+  // Returns an entropy provider that is based on a low entropy source. This
+  // provider is the same type of provider returned by
+  // CreateDefaultEntropyProvider when there's no consent to report metrics, but
+  // will be a new instance.
+  std::unique_ptr<const base::FieldTrial::EntropyProvider>
+  CreateLowEntropyProvider();
 
   // Creates the MetricsStateManager, enforcing that only a single instance
   // of the class exists at a time. Returns NULL if an instance exists already.
   static std::unique_ptr<MetricsStateManager> Create(
       PrefService* local_state,
       EnabledStateProvider* enabled_state_provider,
       const StoreClientInfoCallback& store_client_info,
       const LoadClientInfoCallback& load_client_info);
 
   // Registers local state prefs used by this class.
@@ skipping 88 matching lines @@
   EntropySourceType entropy_source_returned_;
 
   std::unique_ptr<ClonedInstallDetector> cloned_install_detector_;
 
   DISALLOW_COPY_AND_ASSIGN(MetricsStateManager);
 };
 
 }  // namespace metrics
 
 #endif  // COMPONENTS_METRICS_METRICS_STATE_MANAGER_H_