Store field trial parameters in shared memory

base/metrics/field_trial_param_associator.h

Index: base/metrics/field_trial_param_associator.h
diff --git a/base/metrics/field_trial_param_associator.h b/base/metrics/field_trial_param_associator.h
index 214e146966eebbdf8fe0888f4c705eea1f251fb0..eba49abf56c6bdd7528d9842a4916f5d663dc738 100644
--- a/base/metrics/field_trial_param_associator.h
+++ b/base/metrics/field_trial_param_associator.h
@@ -33,10 +33,20 @@ class BASE_EXPORT FieldTrialParamAssociator {
                                  const std::string& group_name,
                                  const FieldTrialParams& params);
 
-  // Gets the parameters for a field trial and its chosen group.
+  // Gets the parameters for a field trial. If the parameters are not in the
+  // mapping, then check the field trial entry in shared memory for the
+  // parameters and cache them here. This version of the API doesn't activate
+  // the trial, which is what we want, since serializing to child processes
+  // shouldn't activate the trial.
   bool GetFieldTrialParams(const std::string& trial_name,
                            FieldTrialParams* params);
 
+  // Same as above, except doesn't search in FieldTrialList for the group name,
+  // since that can cause a deadlock if calling from FieldTrialList.
+  bool GetFieldTrialParamsWithGroupName(const std::string& trial_name,
+                                        const std::string& group_name,
+                                        FieldTrialParams* params);
+
   // Clears the internal field_trial_params_ mapping.
   void ClearAllParamsForTesting();
 
@@ -46,6 +56,17 @@ class BASE_EXPORT FieldTrialParamAssociator {
   // (field_trial_name, field_trial_group)
   typedef std::pair<std::string, std::string> FieldTrialKey;
 
+  // Looks up the field trial entry in shared memory and gets the params from
+  // there.
+  bool GetParamsFromSharedMemory(const std::string& trial_name,
+                                 const std::string& group_name,
+                                 FieldTrialParams* params);
+
+  // Sets the parameters for |trial_name| and |group_name|. Caller must lock.
+  bool AssociateParamsWhileLocked(const std::string& trial_name,
+                                  const std::string& group_name,
+                                  const FieldTrialParams& params);
+
   Lock lock_;
   std::map<FieldTrialKey, FieldTrialParams> field_trial_params_;