[omnibox] Add field trial config for Refined Focus UI experiments

Bug: 1129612
Change-Id: I12d09d4699505b26df91058a9bbf74f3cb2f0e54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2590507Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Reviewed-by: Caitlin Fischer <caitlinfischer@google.com>
Commit-Queue: Caitlin Fischer <caitlinfischer@google.com>
Auto-Submit: Angela Yoeurng <yoangela@chromium.org>
Cr-Commit-Position: refs/heads/master@{#837654}

testing/variations/fieldtrial_testing_config.json

@@ -5123,6 +5123,24 @@
             ]
         }
     ],
+    "OmniboxRefinedFocusStateDesktop": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "OmniboxRefinedFocusState"
+                    ]
+                }
+            ]
+        }
+    ],
     "OmniboxSearchEngineLogoAndroid": [
         {
             "platforms": [