Add testing variation for ReloadSadTab

Bug: none
Change-Id: Id47a70da1b939512fe893c64819daac7545f28e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2074440
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#744770}

testing/variations/fieldtrial_testing_config.json

@@ -2595,6 +2595,21 @@
             ]
         }
     ],
+    "IOSReloadSadTab": [
+        {
+            "platforms": [
+                "ios"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "ReloadSadTab"
+                    ]
+                }
+            ]
+        }
+    ],
     "IOSSSLCommittedInterstitials": [
         {
             "platforms": [