[base] Add MessagePumpMacDelayedWorkOptimizations to fieldtrial_testi…

…ng_config.json.

This is necessary to experiment on Beta.

Bug: 1335524
Change-Id: I83c249b7cf311bfa7436f89d07470fcdd01fb436
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3726422
Reviewed-by: Olivier Li <olivierli@chromium.org>
Auto-Submit: Francois Pierre Doray <fdoray@chromium.org>
Commit-Queue: Olivier Li <olivierli@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1018794}

testing/variations/fieldtrial_testing_config.json

@@ -5527,6 +5527,21 @@
             ]
         }
     ],
+    "MessagePumpMacDelayedWorkOptimizations": [
+        {
+            "platforms": [
+                "mac"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled",
+                    "enable_features": [
+                        "MessagePumpMacDelayedWorkOptimizations"
+                    ]
+                }
+            ]
+        }
+    ],
     "MessagesPreinstall": [
         {
             "platforms": [