Re-land: "Use an explicit identifier in Config"

webrtc/test/common_unittest.cc

Index: webrtc/test/common_unittest.cc
diff --git a/webrtc/test/common_unittest.cc b/webrtc/test/common_unittest.cc
index 082c18c2c7d9361fde111a1880e078bbf050edb7..a239dade73fdadebfcece97614805d6003869d5f 100644
--- a/webrtc/test/common_unittest.cc
+++ b/webrtc/test/common_unittest.cc
@@ -15,6 +15,7 @@ namespace webrtc {
 namespace {
 
 struct MyExperiment {
+  static const ConfigOptionID identifier = ConfigOptionID::kMyExperimentForTest;
   static const int kDefaultFactor;
   static const int kDefaultOffset;
 
@@ -56,6 +57,8 @@ TEST(Config, SetNullSetsTheOptionBackToDefault) {
 }
 
 struct Algo1_CostFunction {
+  static const ConfigOptionID identifier =
+      ConfigOptionID::kAlgo1CostFunctionForTest;
   Algo1_CostFunction() {}
 
   virtual int cost(int x) const {