Actually update FieldTrialEntry's activated field

base/metrics/field_trial.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.
 
 // FieldTrial is a class for handling details of statistical experiments
 // performed by actual users in the field (i.e., in a shipped or beta product).
 // All code is called exclusively on the UI thread currently.
 //
 // The simplest example is an experiment to see whether one of two options
 // produces "better" results across our user population.  In that scenario, UMA
@@ skipping 251 matching lines @@
   // Returns the trial name and selected group name for this field trial via
   // the output parameter |field_trial_state|, but only if the trial has not
   // been disabled. In that case, true is returned and |field_trial_state| is
   // filled in; otherwise, the result is false and |field_trial_state| is left
   // untouched.
   bool GetState(State* field_trial_state);
 
   // Adds the field trial to the allocator whose memory is to be shared with
   // child processes. Assumes the calling code has a lock around the call to
   // this function, since the check for the allocator is not thread-safe.
-  void AddToAllocatorWhileLocked(
-      base::SharedPersistentMemoryAllocator* allocator);
+  void AddToAllocatorWhileLocked(SharedPersistentMemoryAllocator* allocator);
 
   // Returns the group_name. A winner need not have been chosen.
   std::string group_name_internal() const { return group_name_; }
 
   // The name of the field trial, as can be found via the FieldTrialList.
   const std::string trial_name_;
 
   // The maximum sum of all probabilities supplied, which corresponds to 100%.
   // This is the scaling factor used to adjust supplied probabilities.
   const Probability divisor_;
@@ skipping 32 matching lines @@
   bool group_reported_;
 
   // Whether this trial is registered with the global FieldTrialList and thus
   // should notify it when its group is queried.
   bool trial_registered_;
 
   // When benchmarking is enabled, field trials all revert to the 'default'
   // group.
   static bool enable_benchmarking_;
 
+  // Reference to related field trial struct and data in shared memory.
+  SharedPersistentMemoryAllocator::Reference ref_;

[Alexei Svitkine (slow), 2016/10/25 19:18:53]

Nit: Move this above the static var above - so all the non-static members are
together.

[lawrencewu, 2016/10/25 20:27:33]

Done.

+
   DISALLOW_COPY_AND_ASSIGN(FieldTrial);
 };
 
 //------------------------------------------------------------------------------
 // Class with a list of all active field trials.  A trial is active if it has
 // been registered, which includes evaluating its state based on its probaility.
 // Only one instance of this class exists.
 class BASE_EXPORT FieldTrialList {
  public:
   // Year that is guaranteed to not be expired when instantiating a field trial
@@ skipping 183 matching lines @@
 
   // Remove an observer.
   static void RemoveObserver(Observer* observer);
 
   // Notify all observers that a group has been finalized for |field_trial|.
   static void NotifyFieldTrialGroupSelection(FieldTrial* field_trial);
 
   // Return the number of active field trials.
   static size_t GetFieldTrialCount();
 
+  // Return the field trial allocator (for adding to it).
+  static SharedPersistentMemoryAllocator* GetFieldTrialAllocator();
+
  private:
   // Allow tests to access our innards for testing purposes.
   FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest, InstantiateAllocator);
   FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest, AddTrialsToAllocator);
 
   // Expects a mapped piece of shared memory |shm| that was created from the
   // browser process's field_trial_allocator and shared via the command line.
   // This function recreates the allocator, iterates through all the field
   // trials in it, and creates them via CreateFieldTrial().
   static void CreateTrialsFromSharedMemory(
@@ skipping 37 matching lines @@
   // Entropy provider to be used for one-time randomized field trials. If NULL,
   // one-time randomization is not supported.
   std::unique_ptr<const FieldTrial::EntropyProvider> entropy_provider_;
 
   // List of observers to be notified when a group is selected for a FieldTrial.
   scoped_refptr<ObserverListThreadSafe<Observer> > observer_list_;
 
   // Allocator used to instantiate field trial in child processes. In the
   // future, we may want to move this to a more generic place if we want to
   // start passing more data other than field trials.
-  std::unique_ptr<base::SharedPersistentMemoryAllocator>
-      field_trial_allocator_ = nullptr;
+  std::unique_ptr<SharedPersistentMemoryAllocator> field_trial_allocator_ =
+      nullptr;
 
 #if defined(OS_WIN)
   // Readonly copy of the handle to the allocator. Needs to be a member variable
   // because it's needed from both CopyFieldTrialStateToFlags() and
   // AppendFieldTrialHandleIfNeeded().
   HANDLE readonly_allocator_handle_ = nullptr;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialList);
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_FIELD_TRIAL_H_