Backport some tests in /chrome/browser/chromeos/policy to SingleThreadTaskEnvironment

These tests were previously migrated from single-threaded MessageLoop to
a multi-threaded TaskEnvironment (then named ScopedTaskEnvironment) as
part of crbug.com/891670.

//base OWNERS decided in retrospect that it was better to keep a
single-threaded option for TaskEnvironment and introduced
SingleThreadTaskEnvironment. This CL retrofits that decision for
/chrome/browser/chromeos/policy.

This CL is a no-op if it passes CQ.

This CL was uploaded by git cl split.

R=antrim@chromium.org

Bug: 891670
Change-Id: If003533b375a502c364fe87b05ee261a03d1f5f3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787109
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Denis Kuznetsov <antrim@chromium.org>
Commit-Queue: Denis Kuznetsov <antrim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694202}

chrome/browser/chromeos/policy/android_management_client_unittest.cc

@@ -62,7 +62,7 @@ class AndroidManagementClientTest : public testing::Test {
   // Protobuf is used in successfil responsees.
   em::DeviceManagementResponse android_management_response_;
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   MockDeviceManagementService service_;
   StrictMock<base::MockCallback<AndroidManagementClient::StatusCallback>>
       callback_observer_;

chrome/browser/chromeos/policy/cloud_external_data_manager_base_unittest.cc

@@ -93,7 +93,7 @@ class CloudExternalDataManagerBaseTest : public testing::Test {
                        const std::string& repsonse_data,
                        net::HttpStatusCode response_code);
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   base::ScopedTempDir temp_dir_;
   std::unique_ptr<ResourceCache> resource_cache_;
   MockCloudPolicyStore cloud_policy_store_;

chrome/browser/chromeos/policy/server_backed_state_keys_broker_unittest.cc

@@ -44,7 +44,7 @@ class ServerBackedStateKeysBrokerTest : public testing::Test {
   }
 
  protected:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   base::ScopedMockTimeMessageLoopTaskRunner mocked_main_runner_;
   chromeos::FakeSessionManagerClient fake_session_manager_client_;
   ServerBackedStateKeysBroker broker_;

chrome/browser/chromeos/policy/user_cloud_policy_store_chromeos_unittest.cc

@@ -121,7 +121,8 @@ class FakeSessionManagerClient : public chromeos::FakeSessionManagerClient {
 class UserCloudPolicyStoreChromeOSTest : public testing::Test {
  protected:
   UserCloudPolicyStoreChromeOSTest()
-      : task_environment_(base::test::TaskEnvironment::MainThreadType::UI) {}
+      : task_environment_(
+            base::test::SingleThreadTaskEnvironment::MainThreadType::UI) {}
 
   void SetUp() override {
     ASSERT_TRUE(tmp_dir_.CreateUniqueTempDir());
@@ -237,7 +238,7 @@ class UserCloudPolicyStoreChromeOSTest : public testing::Test {
     return GetUserPolicyKeyFile(user_policy_dir(), cryptohome_id_);
   }
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   chromeos::FakeCryptohomeClient cryptohome_client_;
   std::unique_ptr<FakeSessionManagerClient> session_manager_client_;
   UserPolicyBuilder policy_;