Control TaskScheduler initialization params in renderers via field trial.

components/task_scheduler_util/common/BUILD.gn

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 static_library("common") {
   sources = [
     "variations_util.cc",
     "variations_util.h",
   ]
 
   deps = [
     "//base",
+    "//components/variations",
   ]
 }
 
 source_set("unit_tests") {
   testonly = true
   sources = [
     "variations_util_unittest.cc",
   ]
   deps = [
     ":common",
     "//base",
+    "//components/variations",
     "//testing/gtest",
   ]
 }