Mojo: Replace TestWithIOThreadBase with just a helper TestIOThread class.

mojo/system/test_utils.cc

Index: mojo/system/test_utils.cc
diff --git a/mojo/system/test_utils.cc b/mojo/system/test_utils.cc
index 673b36ee4304509a3a7f3cd4dbc6ee46b83d6e60..8e9cbb865a24dc6e74414a332bd13db0d821cd0a 100644
--- a/mojo/system/test_utils.cc
+++ b/mojo/system/test_utils.cc
@@ -31,20 +31,14 @@ void PostTaskAndWait(scoped_refptr<base::TaskRunner> task_runner,
   event.Wait();
 }
 
-// TestWithIOThreadBase --------------------------------------------------------
+// TestIOThread ----------------------------------------------------------------
 
-TestWithIOThreadBase::TestWithIOThreadBase() : io_thread_("io_thread") {
-}
-
-TestWithIOThreadBase::~TestWithIOThreadBase() {
-}
-
-void TestWithIOThreadBase::SetUp() {
+TestIOThread::TestIOThread() : io_thread_("test_io_thread") {
   io_thread_.StartWithOptions(
       base::Thread::Options(base::MessageLoop::TYPE_IO, 0));
 }
 
-void TestWithIOThreadBase::TearDown() {
+TestIOThread::~TestIOThread() {
   io_thread_.Stop();
 }