[omnibox] add ios on device head suggest LE setup to fieldtrial testing

config.

Bug: 925072
Change-Id: I98478cdc4db2cc7c21155bbd1333656f11e1748a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1885391Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Ce Chen <cch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#710156}

testing/variations/fieldtrial_testing_config.json

@@ -4022,6 +4022,21 @@
             ]
         }
     ],
+    "OmniboxOnDeviceHeadSuggestIOS": [
+        {
+            "platforms": [
+                "ios"
+            ],
+            "experiments": [
+                {
+                    "name": "Beta_OnDeviceHeadSuggest_Enabled",
+                    "enable_features": [
+                        "OmniboxOnDeviceHeadProvider"
+                    ]
+                }
+            ]
+        }
+    ],
     "OmniboxSteadyStateElisions": [
         {
             "platforms": [