Add IOSRestoreGaiaCookies to fieldtrial_testing_config.json.

Bug: 1131027
Change-Id: I66fb4bd7e41798cca4f693b8dff01167462dc673
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2568277Reviewed-by: Brian White <bcwhite@chromium.org>
Commit-Queue: Nohemi Fernandez <fernandex@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833244}

testing/variations/fieldtrial_testing_config.json

@@ -3575,6 +3575,21 @@
             ]
         }
     ],
+    "IOSRestoreGaiaCookies": [
+        {
+            "platforms": [
+                "ios"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "RestoreGAIACookiesIfDeleted"
+                    ]
+                }
+            ]
+        }
+    ],
     "Identifiability": [
         {
             "platforms": [