Add fieldtrial config for V8 serialize options.

testing/variations/fieldtrial_testing_config_mac.json

 {
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
@@ skipping 224 matching lines @@
         }
     ],
     "TokenBinding": [
         {
             "enable_features": [
                 "token-binding"
             ],
             "group_name": "TokenBinding"
         }
     ],
+    "V8SerializeOptions": [
+        {
+            "enable_features": [
+                "V8_Serialize_Eager",
+                "V8_Serialize_Age_Code"
+            ],
+            "group_name": "SerializeEagerAndAgeCode"
+        }
+    ],
     "VarationsServiceControl": [
         {
             "group_name": "Interval_30min",
             "params": {
                 "fetch_period_min": "30"
             }
         }
     ],
     "ViewsSimplifiedFullscreenUI": [
         {
@@ skipping 28 matching lines @@
     ],
     "use-new-media-cache": [
         {
             "enable_features": [
                 "use-new-media-cache"
             ],
             "group_name": "Enabled"
         }
     ]
 }