Add simpler API for changing parameters in tests.

components/variations/variations_associated_data.cc

Index: components/variations/variations_associated_data.cc
diff --git a/components/variations/variations_associated_data.cc b/components/variations/variations_associated_data.cc
index 9aa51d379f3d884a094d208d621e0d4eaacbe7f8..9532121d7047c7d9b7ffa2a3458af8db714f665f 100644
--- a/components/variations/variations_associated_data.cc
+++ b/components/variations/variations_associated_data.cc
@@ -11,11 +11,15 @@
 #include "base/feature_list.h"
 #include "base/macros.h"
 #include "base/memory/singleton.h"
+#include "components/variations/entropy_provider.h"
 
 namespace variations {
 
 namespace {
 
+const char kGroupTesting[] = "Testing";
+const char kEntropy[] = "test-entropy-seed";
+
 // The internal singleton accessor for the map, used to keep it thread-safe.
 class GroupMapAccessor {
  public:
@@ -252,6 +256,27 @@ std::string GetVariationParamValueByFeature(const base::Feature& feature,
 // They simply wrap existing functions in this file.
 namespace testing {
 
+VariationParamsManager::VariationParamsManager(
+    const std::string& trial_name,
+    const std::map<std::string, std::string>& params) {
+  SetVariationParams(trial_name, params);
+}
+
+VariationParamsManager::~VariationParamsManager() {
+  ClearAllVariationIDs();
+  ClearAllVariationParams();
+  field_trial_list_.reset();
+}
+
+void VariationParamsManager::SetVariationParams(
+    const std::string& trial_name,
+    const std::map<std::string, std::string>& params) {
+  field_trial_list_.reset(
+      new base::FieldTrialList(new metrics::SHA1EntropyProvider(kEntropy)));

[Alexei Svitkine (slow), 2016/07/15 14:51:01]

You can just pass nullptr here.

[jkrcal, 2016/07/18 13:09:01]

Done.

+  variations::AssociateVariationParams(trial_name, kGroupTesting, params);
+  base::FieldTrialList::CreateFieldTrial(trial_name, kGroupTesting);
+}
+
 void ClearAllVariationIDs() {
   GroupMapAccessor::GetInstance()->ClearAllMapsForTesting();
 }