[Extensions Toolbar] Add a finch config for the redesign

testing/variations/fieldtrial_testing_config_win.json

 {
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutomaticTabDiscarding": [
         {
             "group_name": "Enabled"
         }
@@ skipping 26 matching lines @@
     "EnableGoogleCachedCopyTextExperiment": [
         {
             "group_name": "Button"
         }
     ],
     "EnableSessionCrashedBubbleUI": [
         {
             "group_name": "Enabled"
         }
     ],
+    "ExtensionActionRedesign": [
+        {
+            "group_name": "Enabled"
+        }
+    ],
     "ExtensionContentVerification": [
         {
             "group_name": "Enforce"
         }
     ],
     "ExtensionInstallVerification": [
         {
             "group_name": "Enforce"
         }
     ],
@@ skipping 144 matching lines @@
     ],
     "VarationsServiceControl": [
         {
             "group_name": "Interval_30min",
             "params": {
                 "fetch_period_min": "30"
             }
         }
     ]
 }