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 +221,76 @@
   EXPECT_EQ(default_group_name, trial->group_name());
 }
 
+TEST_F(FieldTrialTest, HashName) {
+  // Make sure hashing is stable on all platforms.
+  struct {
+    const char* name;
+    uint32 hash_value;
+  } known_hashes[] = {
+    {"a", 937752454},
+    {"1", 723085877},
+    {"Trial Name", 2713117220},
+    {"Group Name", 3201815843},
+    {"My Favorite Experiment", 3722155194},
+    {"My Awesome Group Name", 4109503236},
+    {"abcdefghijklmonpqrstuvwxyz", 787728696},
+    {"0123456789ABCDEF", 348858318}
+  };
+  for (size_t i = 0; i < ARRAYSIZE_UNSAFE(known_hashes); ++i) {
+    EXPECT_EQ(known_hashes[i].hash_value,
+              FieldTrial::HashName(known_hashes[i].name));
+  }
+}
+
+TEST_F(FieldTrialTest, NameGroupIds) {
+  std::string no_group("No Group");
+  uint32 no_group_id = FieldTrial::HashName(no_group);
+  scoped_refptr<FieldTrial> trial(new FieldTrial(
+      no_group, 10, "Default", next_year_, 12, 31));
+
+  // There is no winner yet, so no NameGroupId should be returned.
+  FieldTrial::NameGroupId name_group_id;
+  EXPECT_FALSE(trial->GetNameGroupId(&name_group_id));
+
+  // Create a single winning group.
+  std::string one_winner("One Winner");
+  uint32 one_winner_id = FieldTrial::HashName(one_winner);
+  trial = new FieldTrial(one_winner, 10, "Default", next_year_, 12, 31);
+  std::string winner("Winner");
+  uint32 winner_group_id = FieldTrial::HashName(winner);
+  trial->AppendGroup(winner, 10);
+  EXPECT_TRUE(trial->GetNameGroupId(&name_group_id));
+  EXPECT_EQ(one_winner_id, name_group_id.name);
+  EXPECT_EQ(winner_group_id, name_group_id.group);
+
+  std::string multi_group("MultiGroup");
+  uint32 multi_group_id = FieldTrial::HashName(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->GetNameGroupId(&name_group_id));
+  EXPECT_EQ(multi_group_id, name_group_id.name);
+  uint32 multi_group_winner_id =
+      FieldTrial::HashName(multi_group_trial->group_name());
+  EXPECT_EQ(multi_group_winner_id, name_group_id.group);
+
+  // Now check if the list is built properly...
+  std::vector<FieldTrial::NameGroupId> name_group_ids;
+  FieldTrialList::GetFieldTrialNameGroupIds(&name_group_ids);
+  EXPECT_EQ(2U, name_group_ids.size());
+  for (size_t i = 0; i < name_group_ids.size(); ++i) {
+    // Order is not guaranteed, so check all values.
+    EXPECT_NE(no_group_id, name_group_ids[i].name);
+    EXPECT_TRUE(one_winner_id != name_group_ids[i].name ||
+                winner_group_id == name_group_ids[i].group);
+    EXPECT_TRUE(multi_group_id != name_group_ids[i].name ||
+                multi_group_winner_id == name_group_ids[i].group);
+  }
+}
+
 TEST_F(FieldTrialTest, Save) {
   std::string save_string;