Reland^3 [task] Add UseUtilityThreadGroup to testing config"

This is a reland of commit d7c1e9df7ffb98f9ec7fc7044a927c9967c6b7a6

Original change's description:
> Reland^2 [task] Add UseUtilityThreadGroup to testing config
>
> Reland of https://chromium-review.googlesource.com/c/chromium/src/+/4342013
> Reason for revert: regression of wasm benchmark in jetstream
>
> Regression should be fixed with https://chromium-review.googlesource.com/c/v8/v8/+/5349727
>
> Bug: 1366240
> Change-Id: I95c22b42dfc55d5985227fef4964ff1e44c0097f
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5353546
> Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
> Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1272183}

Bug: 1366240
Change-Id: Ifabda8c59d993ad0b434c867d749457ba40652da
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5385709
Commit-Queue: Etienne Pierre-Doray <etiennep@chromium.org>
Reviewed-by: Francois Pierre Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1277776}
diff --git a/testing/variations/fieldtrial_testing_config.json b/testing/variations/fieldtrial_testing_config.json
index 687281e..7d23c7e 100644
--- a/testing/variations/fieldtrial_testing_config.json
+++ b/testing/variations/fieldtrial_testing_config.json
@@ -19301,6 +19301,33 @@
             ]
         }
     ],
+    "UseUtilityThreadGroup": [
+        {
+            "platforms": [
+                "android",
+                "android_weblayer",
+                "android_webview",
+                "chromeos",
+                "chromeos_lacros",
+                "fuchsia",
+                "ios",
+                "linux",
+                "mac",
+                "windows"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "UseUtilityThreadGroup",
+                        "V8ConcurrentMaglevHighPriorityThreads",
+                        "V8ConcurrentMarkingHighPriorityThreads",
+                        "V8ConcurrentSparkplugHighPriorityThreads"
+                    ]
+                }
+            ]
+        }
+    ],
     "UseV1MetricsTerminationHoldback": [
         {
             "platforms": [