Remove an unnecessary field trial look up when using params.

This should speed up using feature / field trial params APIs.

Bug: 1163921
Change-Id: Ieacd216cba47c259287b3b392bd00fa7077ac084
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2615481
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Auto-Submit: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#841559}

base/metrics/field_trial_param_associator.cc

@@ -39,16 +39,13 @@ bool FieldTrialParamAssociator::AssociateFieldTrialParams(
   return true;
 }
 
-bool FieldTrialParamAssociator::GetFieldTrialParams(
-    const std::string& trial_name,
+bool FieldTrialParamAssociator::GetFieldTrialParams(FieldTrial* field_trial,
                                                     FieldTrialParams* params) {
-  FieldTrial* field_trial = FieldTrialList::Find(trial_name);
   if (!field_trial)
     return false;
-
   // First try the local map, falling back to getting it from shared memory.
-  if (GetFieldTrialParamsWithoutFallback(trial_name, field_trial->group_name(),
-                                         params)) {
+  if (GetFieldTrialParamsWithoutFallback(field_trial->trial_name(),
+                                         field_trial->group_name(), params)) {
     return true;
   }
 

base/metrics/field_trial_param_associator.h

@@ -33,9 +33,9 @@ class BASE_EXPORT FieldTrialParamAssociator {
                                  const FieldTrialParams& params);
 
   // Gets the parameters for a field trial and its chosen group. If not found in
-  // field_trial_params_, then tries to looks it up in shared memory.
-  bool GetFieldTrialParams(const std::string& trial_name,
-                           FieldTrialParams* params);
+  // field_trial_params_, then tries to looks it up in shared memory. Returns
+  // false if no params are available or the passed |field_trial| is null.
+  bool GetFieldTrialParams(FieldTrial* field_trial, FieldTrialParams* params);
 
   // Gets the parameters for a field trial and its chosen group. Does not
   // fallback to looking it up in shared memory. This should only be used if you

base/metrics/field_trial_params.cc

@@ -86,8 +86,9 @@ bool AssociateFieldTrialParamsFromString(
 
 bool GetFieldTrialParams(const std::string& trial_name,
                          FieldTrialParams* params) {
-  return FieldTrialParamAssociator::GetInstance()->GetFieldTrialParams(
-      trial_name, params);
+  FieldTrial* trial = FieldTrialList::Find(trial_name);
+  return FieldTrialParamAssociator::GetInstance()->GetFieldTrialParams(trial,
+                                                                       params);
 }
 
 bool GetFieldTrialParamsByFeature(const Feature& feature,
@@ -96,10 +97,8 @@ bool GetFieldTrialParamsByFeature(const Feature& feature,
     return false;
 
   FieldTrial* trial = FeatureList::GetFieldTrial(feature);
-  if (!trial)
-    return false;
-
-  return GetFieldTrialParams(trial->trial_name(), params);
+  return FieldTrialParamAssociator::GetInstance()->GetFieldTrialParams(trial,
+                                                                       params);
 }
 
 std::string GetFieldTrialParamValue(const std::string& trial_name,

base/metrics/field_trial_unittest.cc

@@ -1275,8 +1275,7 @@ TEST_F(FieldTrialListTest, AssociateFieldTrialParams) {
 
   // Check that we fetch the param from shared memory properly.
   std::map<std::string, std::string> new_params;
-  FieldTrialParamAssociator::GetInstance()->GetFieldTrialParams(trial_name,
-                                                                &new_params);
+  GetFieldTrialParams(trial_name, &new_params);
   EXPECT_EQ("value1", new_params["key1"]);
   EXPECT_EQ("value2", new_params["key2"]);
   EXPECT_EQ(2U, new_params.size());
@@ -1315,8 +1314,7 @@ TEST_F(FieldTrialListTest, MAYBE_ClearParamsFromSharedMemory) {
 
     // Check that there are no params associated with the field trial anymore.
     std::map<std::string, std::string> new_params;
-    FieldTrialParamAssociator::GetInstance()->GetFieldTrialParams(trial_name,
-                                                                  &new_params);
+    GetFieldTrialParams(trial_name, &new_params);
     EXPECT_EQ(0U, new_params.size());
 
     // Now duplicate the handle so we can easily check that the trial is still