Enable BrowserScheduler.RedirectHistoryService experiment on trunk.

testing/variations/fieldtrial_testing_config.json

 {
     "AndroidSessionNotifications": [
         {
             "platforms": [
                 "android"
             ],
             "experiments": [
                 {
                     "name": "Disabled"
                 }
@@ skipping 196 matching lines @@
                 "chromeos",
                 "ios",
                 "linux",
                 "mac",
                 "win"
             ],
             "experiments": [
                 {
                     "name": "Default",
                     "params": {
+                        "RedirectHistoryService": "true",
                         "RedirectSequencedWorkerPools": "true"
                     }
                 },
                 {
                     "name": "EnableViaFlag",
                     "forcing_flag": "enable-browser-task-scheduler",
                     "params": {
                         "RedirectHistoryService": "true",
                         "RedirectNonUINonIOBrowserThreads": "true",
                         "RedirectSequencedWorkerPools": "true"
@@ skipping 2300 matching lines @@
                 {
                     "name": "Enabled",
                     "enable_features": [
                         "use-new-media-cache"
                     ]
                 }
             ]
         }
     ]
 }