[Variations] Add groups to the testing configurations.

testing/variations/fieldtrial_testing_config_win.json

 {
     "BrowserBlacklist": [
         {
             "group_name": "Enabled"
         }
     ],
     "ChildAccountDetection": [
         {
             "group_name": "Disabled"
         }
@@ skipping 100 matching lines @@
             "group_name": "Enabled"
         }
     ],
     "SyncHttpContentCompression": [
         {
             "group_name": "Enabled"
         },
         {
             "group_name": "Disabled"
         }
+    ],
+    "AutofillFieldMetadata": [
+        {
+            "group_name": "Enabled"
+        }
     ]
 }