Add Finch testing config for PasswordBranding

testing/variations/fieldtrial_testing_config_win.json

 {
     "AsyncSetAsDefault": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
@@ skipping 121 matching lines @@
                 "WiFi.DefaultMedianKbps": "2736",
                 "WiFi.DefaultMedianRTTMsec": "168"
             }
         }
     ],
     "NewProfileManagement": [
         {
             "group_name": "Enabled"
         }
     ],
+    "PasswordBranding": [
+        {
+            "group_name": "SmartLockBranding"
+        }
+    ],
     "PasswordGeneration": [
         {
             "group_name": "Disabled"
         }
     ],
     "QUIC": [
         {
             "group_name": "Enabled",
             "params": {
                 "alternate_protocol_probability_threshold": "0.01"
@@ skipping 116 matching lines @@
         {
             "group_name": "Enabled"
         }
     ],
     "WebRTC-PeerConnectionDTLS1.2": [
         {
             "group_name": "Enabled"
         }
     ]
 }