Remove references of MessageLoopForIO in /base

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=kylechar@chromium.org

Change-Id: Ib3a70b497ba1117d20f30399903e40ce204f996f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733534
Auto-Submit: Carlos Caballero <carlscab@google.com>
Reviewed-by: kylechar <kylechar@chromium.org>
Commit-Queue: kylechar <kylechar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683736}

base/logging_unittest.cc

@@ -11,11 +11,11 @@
 #include "base/files/scoped_temp_dir.h"
 #include "base/logging.h"
 #include "base/macros.h"
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/sanitizer_buildflags.h"
 #include "base/strings/string_piece.h"
 #include "base/test/scoped_feature_list.h"
+#include "base/test/scoped_task_environment.h"
 #include "build/build_config.h"
 
 #include "testing/gmock/include/gmock/gmock.h"
@@ -93,7 +93,8 @@ class LogStateSaver {
 
 class LoggingTest : public testing::Test {
  private:
-  base::MessageLoopForIO message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_{
+      base::test::ScopedTaskEnvironment::MainThreadType::IO};
   LogStateSaver log_state_saver_;
 };