Change variant of BlinkSchedulerPerAgentSchedulingExperiments.

Bug: 1113134, 1115389
Change-Id: I72a5de9c4fd7914c7c4621c61198a813c7249193
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2351642Reviewed-by: Trent Apted <tapted@chromium.org>
Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Tal Pressman <talp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#797505}

testing/variations/fieldtrial_testing_config.json

@@ -1129,6 +1129,7 @@
             "platforms": [
                 "android",
                 "android_weblayer",
+                "chromeos",
                 "ios",
                 "linux",
                 "mac",
@@ -1136,10 +1137,10 @@
             ],
             "experiments": [
                 {
-                    "name": "disable_timer-queues_until_onload",
+                    "name": "best-effort_timer-queues_until_onload",
                     "params": {
                         "delay_ms": "0",
-                        "method": "disable",
+                        "method": "best-effort",
                         "queues": "timer-queues",
                         "signal": "onload"
                     },