Store field trial parameters in shared memory

base/metrics/field_trial_param_associator.cc

Index: base/metrics/field_trial_param_associator.cc
diff --git a/base/metrics/field_trial_param_associator.cc b/base/metrics/field_trial_param_associator.cc
index b96cc396df874689af034691d9479a780ae78417..9531e13afb78a7f6f560fe465717a0f368f2c8eb 100644
--- a/base/metrics/field_trial_param_associator.cc
+++ b/base/metrics/field_trial_param_associator.cc
@@ -37,9 +37,28 @@ bool FieldTrialParamAssociator::AssociateFieldTrialParams(
 bool FieldTrialParamAssociator::GetFieldTrialParams(
     const std::string& trial_name,
     FieldTrialParams* params) {
+  FieldTrial* field_trial = FieldTrialList::Find(trial_name);
+  if (!field_trial)
+    return false;
+
+  // We try looking for the params in field_trial_params_ via
+  // GetFieldTrialParamsWithoutFallback. If it's not there, then try to look it

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

Nit: The first sentence doesn't add much to the comment.

How about merging the two sentences into something more concise, such as:

// First try the local map, falling back to getting it from shared memory.

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

Done.

+  // up in shared memory.
+  if (GetFieldTrialParamsWithoutFallback(trial_name, field_trial->group_name(),
+                                         params)) {
+    return true;
+  }
+
+  // TODO(lawrencewu): add the params to field_trial_params_ for next time.
+  return FieldTrialList::GetParamsFromSharedMemory(field_trial, params);
+}
+
+bool FieldTrialParamAssociator::GetFieldTrialParamsWithoutFallback(
+    const std::string& trial_name,
+    const std::string& group_name,
+    FieldTrialParams* params) {
   AutoLock scoped_lock(lock_);
 
-  const std::string group_name = FieldTrialList::FindFullName(trial_name);
   const FieldTrialKey key(trial_name, group_name);
   if (!ContainsKey(field_trial_params_, key))
     return false;
@@ -51,6 +70,12 @@ bool FieldTrialParamAssociator::GetFieldTrialParams(
 void FieldTrialParamAssociator::ClearAllParamsForTesting() {
   AutoLock scoped_lock(lock_);
   field_trial_params_.clear();
+  FieldTrialList::ClearParamsFromSharedMemoryForTesting();
+}
+
+void FieldTrialParamAssociator::ClearAllCachedParamsForTesting() {
+  AutoLock scoped_lock(lock_);
+  field_trial_params_.clear();
 }
 
 }  // namespace base