Revert of Use TaskScheduler instead of WorkerPool in nss_cert_database.cc.

chromeos/network/network_cert_migrator_unittest.cc

Index: chromeos/network/network_cert_migrator_unittest.cc
diff --git a/chromeos/network/network_cert_migrator_unittest.cc b/chromeos/network/network_cert_migrator_unittest.cc
index 489cb68dd4245b42e1b49bacd7406797f1f3df2d..006027b0004ff5682ca0b4149846d63a28001d24 100644
--- a/chromeos/network/network_cert_migrator_unittest.cc
+++ b/chromeos/network/network_cert_migrator_unittest.cc
@@ -12,7 +12,6 @@
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
-#include "base/test/scoped_task_scheduler.h"
 #include "chromeos/cert_loader.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #include "chromeos/dbus/shill_profile_client.h"
@@ -49,6 +48,7 @@ class NetworkCertMigratorTest : public testing::Test {
     test_nsscertdb_.reset(new net::NSSCertDatabaseChromeOS(
         crypto::ScopedPK11Slot(PK11_ReferenceSlot(test_nssdb_.slot())),
         crypto::ScopedPK11Slot(PK11_ReferenceSlot(test_nssdb_.slot()))));
+    test_nsscertdb_->SetSlowTaskRunnerForTest(message_loop_.task_runner());
 
     DBusThreadManager::Initialize();
     service_test_ =
@@ -189,7 +189,7 @@ class NetworkCertMigratorTest : public testing::Test {
   scoped_refptr<net::X509Certificate> test_client_cert_;
   std::string test_client_cert_pkcs11_id_;
   std::string test_client_cert_slot_id_;
-  base::test::ScopedTaskScheduler scoped_task_scheduler_;
+  base::MessageLoop message_loop_;
 
  private:
   std::unique_ptr<NetworkStateHandler> network_state_handler_;