Backport some tests in /chrome/browser/safe_browsing/chrome_cleaner 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/safe_browsing/chrome_cleaner.

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

This CL was uploaded by git cl split.

R=joenotcharles@google.com

Bug: 891670
Change-Id: I16c7853ec95cc1aa12416234ec09778b5e1bd840
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787057
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Joe Mason <joenotcharles@google.com>
Commit-Queue: Joe Mason <joenotcharles@google.com>
Cr-Commit-Position: refs/heads/master@{#693734}

chrome/browser/safe_browsing/chrome_cleaner/mock_chrome_cleaner_process_win.cc

@@ -619,7 +619,7 @@ int MockChromeCleanerProcess::Run() {
   if (options_.crash_point() == CrashPoint::kAfterConnection)
     exit(kDeliberateCrashExitCode);
 
-  base::test::TaskEnvironment task_environment;
+  base::test::SingleThreadTaskEnvironment task_environment;
   base::RunLoop run_loop;
   // After the response from the parent process is received, this will post a
   // task to unblock the child process's main thread.