Migrate base::TestIOThread to OnceCallback

base::TestIOThread::PostTask is a left-over of the OnceCallback support
of TaskRunner::PostTask, that is needed by its user to migrate to
OnceCallback.

Bug: 714018
Change-Id: Iceb18fb84bde555e4fa217c32e463e01adf034a1
Reviewed-on: https://chromium-review.googlesource.com/997313Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550135}

base/test/test_io_thread.cc

@@ -38,9 +38,8 @@ void TestIOThread::Stop() {
   io_thread_started_ = false;
 }
 
-void TestIOThread::PostTask(const Location& from_here,
-                            const base::Closure& task) {
-  task_runner()->PostTask(from_here, task);
+void TestIOThread::PostTask(const Location& from_here, base::OnceClosure task) {
+  task_runner()->PostTask(from_here, std::move(task));
 }
 
 }  // namespace base

base/test/test_io_thread.h

@@ -38,7 +38,7 @@ class TestIOThread {
   void Stop();
 
   // Post |task| to the IO thread.
-  void PostTask(const Location& from_here, const base::Closure& task);
+  void PostTask(const Location& from_here, base::OnceClosure task);
 
   base::MessageLoopForIO* message_loop() {
     return static_cast<base::MessageLoopForIO*>(io_thread_.message_loop());