Add and implement API to associate Google experiment IDs with FieldTrials.

base/metrics/field_trial.h

Index: base/metrics/field_trial.h
diff --git a/base/metrics/field_trial.h b/base/metrics/field_trial.h
index 28523934e4ad72d982ac3a33cd794b806ea5352e..be58a9367f0ab258dbfe6100438617bd759bdffd 100644
--- a/base/metrics/field_trial.h
+++ b/base/metrics/field_trial.h
@@ -146,6 +146,10 @@ class BASE_EXPORT FieldTrial : public RefCounted<FieldTrial> {
   static std::string MakeName(const std::string& name_prefix,
                               const std::string& trial_name);
 
+  // Helper function to create a NameGroupId from |trial_name| and |group_name|.
+  static NameGroupId MakeNameGroupId(const std::string& trial_name,
+                                     const std::string& group_name);
+
   // Enable benchmarking sets field trials to a common setting.
   static void EnableBenchmarking();