Tab Search: Add fieldtrial testing config entry

Bug: 1128599
Change-Id: I750430e805510d7ffe065e5b9c9f789d7241dc3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2465489Reviewed-by: Steven Holte <holte@chromium.org>
Commit-Queue: Thomas Lukaszewicz <tluk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816715}

testing/variations/fieldtrial_testing_config.json

@@ -6732,6 +6732,22 @@
             ]
         }
     ],
+    "TabSearch": [
+        {
+            "platforms": [
+                "chromeos"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "TabSearch",
+                        "TabSearchFixedEntrypoint"
+                    ]
+                }
+            ]
+        }
+    ],
     "TabToGTSAnimation": [
         {
             "platforms": [