Backport some tests in /chromeos 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
/chromeos.

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

This CL was uploaded by git cl split.

R=stevenjb@chromium.org

Bug: 891670
Change-Id: I15e676b4edffef703e9bf5455faed25bf9bde646
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787100
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694567}

chromeos/tpm/tpm_token_info_getter_unittest.cc

@@ -226,7 +226,7 @@ class SystemTPMTokenInfoGetterTest : public testing::Test {
   std::vector<int64_t> delays_;
 
  private:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTPMTokenInfoGetterTest);
 };
@@ -252,7 +252,7 @@ class UserTPMTokenInfoGetterTest : public testing::Test {
   std::vector<int64_t> delays_;
 
  private:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
 
   DISALLOW_COPY_AND_ASSIGN(UserTPMTokenInfoGetterTest);
 };