[Sync] Add a fieldtrial testing config for new impl of wallet data sync

Bug: 853688
Change-Id: Idfd02f83693ad4861015d9edd3a9b23c7c6e174c
Reviewed-on: https://chromium-review.googlesource.com/1238175Reviewed-by: Robert Kaplow (sloooow) <rkaplow@chromium.org>
Commit-Queue: Jan Krcal <jkrcal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#593547}

testing/variations/fieldtrial_testing_config.json

@@ -4247,6 +4247,26 @@
             ]
         }
     ],
+    "SyncUSSAutofillWalletData": [
+        {
+            "platforms": [
+                "android",
+                "chromeos",
+                "ios",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "SyncUSSAutofillWalletData"
+                    ]
+                }
+            ]
+        }
+    ],
     "TLS13Variant": [
         {
             "platforms": [