Remove references of MessageLoopForIO in /chrome/renderer/media/cast_ipc_dispatcher_unittest.cc

MessageLoopForIO will go away soon use ScopedTaskEnvironment instead.

ScopedTaskEnvironment will per default start a ThreadPool, which should
be fine in most of the cases. If you believe your test needs to make sure
that no ThreadPool runs let me know and I will update the patch.

BUG=891670
This CL was uploaded by git cl split.

R=miu@chromium.org

Change-Id: I692e8ce91f43e17c5d0ad58dc1b194145490a4d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733613
Commit-Queue: Carlos Caballero <carlscab@google.com>
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: Yuri Wiitala <miu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683976}

chrome/renderer/media/cast_ipc_dispatcher_unittest.cc

@@ -2,11 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "base/message_loop/message_loop.h"
+#include "chrome/renderer/media/cast_ipc_dispatcher.h"
+
+#include "base/test/scoped_task_environment.h"
 #include "base/test/simple_test_tick_clock.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/common/cast_messages.h"
-#include "chrome/renderer/media/cast_ipc_dispatcher.h"
 #include "ipc/ipc_message_macros.h"
 #include "media/cast/logging/logging_defines.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -25,7 +26,8 @@ class CastIPCDispatcherTest : public testing::Test {
   }
 
   scoped_refptr<CastIPCDispatcher> dispatcher_;
-  base::MessageLoopForIO message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_{
+      base::test::ScopedTaskEnvironment::MainThreadType::IO};
 };
 
 TEST_F(CastIPCDispatcherTest, RawEvents) {