Added a Unique ID for a Field Trial containing it's hashed name and the selected group ID.

base/metrics/field_trial_unittest.cc

Index: base/metrics/field_trial_unittest.cc
===================================================================
--- base/metrics/field_trial_unittest.cc	(revision 118842)
+++ base/metrics/field_trial_unittest.cc	(working copy)
@@ -221,6 +221,51 @@
   EXPECT_EQ(default_group_name, trial->group_name());
 }
 
+TEST_F(FieldTrialTest, UIDs) {
+  std::string no_group("No Group");
+  size_t no_group_id = BASE_HASH_NAMESPACE::hash_value(no_group);
+  scoped_refptr<FieldTrial> trial(new FieldTrial(
+      no_group, 10, "Default", next_year_, 12, 31));
+
+  // There is no winner yet, so no UID should be returned for this trial.
+  FieldTrial::UID uid;
+  EXPECT_FALSE(trial->GetUID(&uid));
+
+  // Create a single winning group.
+  std::string one_winner("One Winner");
+  size_t one_winner_id = BASE_HASH_NAMESPACE::hash_value(one_winner);
+  trial = new FieldTrial(one_winner, 10, "Default", next_year_, 12, 31);
+  int winner_group_id = trial->AppendGroup("Winner", 10);
+  EXPECT_TRUE(trial->GetUID(&uid));
+  EXPECT_EQ(one_winner_id, uid.first);
+  EXPECT_EQ(winner_group_id, uid.second);
+
+  std::string multi_group("MultiGroup");
+  size_t multi_group_id = BASE_HASH_NAMESPACE::hash_value(multi_group);
+  scoped_refptr<FieldTrial> multi_group_trial =
+      new FieldTrial(multi_group, 9, "Default", next_year_, 12, 31);
+
+  multi_group_trial->AppendGroup("Me", 3);
+  multi_group_trial->AppendGroup("You", 3);
+  multi_group_trial->AppendGroup("Them", 3);
+  EXPECT_TRUE(multi_group_trial->GetUID(&uid));
+  EXPECT_EQ(multi_group_id, uid.first);
+  EXPECT_EQ(multi_group_trial->group(), uid.second);
+
+  // Now check if the list is built properly...
+  std::vector<FieldTrial::UID> uids;
+  FieldTrialList::GetFieldTrialUIDs(&uids);
+  EXPECT_EQ(2, uids.size());
+  for (size_t i = 0; i < uids.size(); ++i) {
+    // Order is not guaranteed, so check all values.
+    EXPECT_NE(no_group_id, uids[i].first);
+    EXPECT_TRUE(one_winner_id != uids[i].first ||
+                winner_group_id == uids[i].second);
+    EXPECT_TRUE(multi_group_id != uids[i].first ||
+                multi_group_trial->group() == uids[i].second);
+  }
+}
+
 TEST_F(FieldTrialTest, Save) {
   std::string save_string;