Added ResourcePriorities field trial to the waterfall testing config in preparation for launch

testing/variations/fieldtrial_testing_config_mac.json

 {
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
@@ skipping 136 matching lines @@
         {
             "group_name": "ShowAndPossiblySend",
             "params": {
                 "sendingThreshold": "abcdef"
             }
         },
         {
             "group_name": "DontShowAndDontSend"
         }
     ],
+    "ResourcePriorities": [
+        {
+            "group_name": "AllExceptAsyncScripts_11011_1_1_10"
+        },
+        {
+            "group_name": "Control"
+        }
+    ],
     "SafeBrowsingReportPhishingErrorLink": [
         {
             "group_name": "Enabled"
         },
         {
             "group_name": "Control"
         },
         {
             "group_name": "Disabled"
         }
@@ skipping 66 matching lines @@
         {
             "group_name": "Enabled"
         }
     ],
     "WebRTC-PeerConnectionDTLS1.2": [
         {
             "group_name": "Enabled"
         }
     ]
 }