Add variations params api to get params from features.

base/feature_list_unittest.cc

Index: base/feature_list_unittest.cc
diff --git a/base/feature_list_unittest.cc b/base/feature_list_unittest.cc
index b49177f26e37e87a16c9082b1ed9ac63f7552a12..a7e7b71183b32e7e263e4f9c7c47c382d215f56c 100644
--- a/base/feature_list_unittest.cc
+++ b/base/feature_list_unittest.cc
@@ -393,6 +393,19 @@ TEST_F(FeatureListTest, GetFeatureOverrides_UseDefault) {
   EXPECT_EQ("D", SortFeatureListString(disable_features));
 }
 
+TEST_F(FeatureListTest, GetFieldTrial) {
+  ClearFeatureListInstance();
+  FieldTrialList field_trial_list(nullptr);
+  FieldTrial* trial = FieldTrialList::CreateFieldTrial("Trial", "Group");
+  std::unique_ptr<FeatureList> feature_list(new FeatureList);
+  feature_list->RegisterFieldTrialOverride(
+      kFeatureOnByDefaultName, FeatureList::OVERRIDE_USE_DEFAULT, trial);
+  RegisterFeatureListInstance(std::move(feature_list));
+
+  EXPECT_EQ(trial, FeatureList::GetFieldTrial(kFeatureOnByDefault));
+  EXPECT_EQ(nullptr, FeatureList::GetFieldTrial(kFeatureOffByDefault));
+}
+
 TEST_F(FeatureListTest, InitializeFromCommandLine_WithFieldTrials) {
   ClearFeatureListInstance();
   FieldTrialList field_trial_list(nullptr);