Store field trial parameters in shared memory

base/metrics/field_trial.h

Index: base/metrics/field_trial.h
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index 34b9782bee0fe06c51abf1383c3d98c247c4a958..3a5a71c60761675ec3c6a8370e6a822c4d2ff8f1 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -228,6 +228,8 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
 
   friend class RefCounted<FieldTrial>;
 
+  friend class FieldTrialParamAssociator;

[Alexei Svitkine (slow), 2016/11/24 17:56:32]

Can this be removed?

[lawrencewu, 2016/11/24 21:50:36]

Yes, I think so. Removed.

+
   // This is the group number of the 'default' group when a choice wasn't forced
   // by a call to FieldTrialList::CreateFieldTrial. It is kept private so that
   // consumers don't use it by mistake in cases where the group was forced.
@@ -550,12 +552,22 @@ class BASE_EXPORT FieldTrialList {
   // Return the number of active field trials.
   static size_t GetFieldTrialCount();
 
+  // Gets the parameters for |field_trial| from shared memory and stores them in
+  // |params|.

[Alexei Svitkine (slow), 2016/11/24 17:56:32]

Add a second sentence mentioning that this is exposed only for it's used from
FieldTrialParamAssociator and shouldn't be used by anything else.

[lawrencewu, 2016/11/24 21:50:36]

Done.

+  static bool GetParamsFromSharedMemory(
+      FieldTrial* field_trial,
+      std::map<std::string, std::string>* params);
+
+  // Clears all the params in the allocator.
+  static void ClearParamsFromSharedMemoryForTesting();
+
  private:
   // Allow tests to access our innards for testing purposes.
   FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest, InstantiateAllocator);
   FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest, AddTrialsToAllocator);
   FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest,
                            DoNotAddSimulatedFieldTrialsToAllocator);
+  FRIEND_TEST_ALL_PREFIXES(FieldTrialListTest, AssociateFieldTrialParams);
 
 #if defined(OS_WIN)
   // Takes in |handle| that should have been retrieved from the command line and
@@ -608,8 +620,8 @@ class BASE_EXPORT FieldTrialList {
   // FieldTrialList is created after that.
   static bool used_without_global_;
 
-  // Lock for access to registered_.
-  base::Lock lock_;
+  // Lock for access to registered_ and field_trial_allocator_.
+  Lock lock_;
   RegistrationMap registered_;
 
   std::map<std::string, std::string> seen_states_;