[Passwords] Add Field Trial Testing Config for SecondaryServerFieldPredictions

R=kazinova@google.com

Bug: 1148394
Change-Id: Iabf0963d30c293ab739a01a8a639292f89abd300
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2569520
Auto-Submit: Jan Wilken Dörrie <jdoerrie@chromium.org>
Reviewed-by: Maria Kazinova <kazinova@google.com>
Commit-Queue: Jan Wilken Dörrie <jdoerrie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833338}

testing/variations/fieldtrial_testing_config.json

@@ -6410,6 +6410,27 @@
             ]
         }
     ],
+    "SecondaryServerFieldPredictions": [
+        {
+            "platforms": [
+                "android",
+                "android_webview",
+                "chromeos",
+                "ios",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "SecondaryServerFieldPredictions"
+                    ]
+                }
+            ]
+        }
+    ],
     "ServiceManagerForBackgroundPrefetch": [
         {
             "platforms": [