Use ScopedTaskEnvironment instead of MessageLoop in chrome unit tests.

chrome/utility/image_writer/image_writer_unittest.cc

Index: chrome/utility/image_writer/image_writer_unittest.cc
diff --git a/chrome/utility/image_writer/image_writer_unittest.cc b/chrome/utility/image_writer/image_writer_unittest.cc
index d935c36d99b67c63f5165c2c3924a6f0e4b1febb..738a24615e59179c49ef30b96919e320147072f8 100644
--- a/chrome/utility/image_writer/image_writer_unittest.cc
+++ b/chrome/utility/image_writer/image_writer_unittest.cc
@@ -10,6 +10,7 @@
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "chrome/utility/image_writer/error_messages.h"
 #include "chrome/utility/image_writer/image_writer.h"
 #include "chrome/utility/image_writer/image_writer_handler.h"
@@ -53,7 +54,7 @@ class ImageWriterUtilityTest : public testing::Test {
   base::FilePath device_path_;
 
  private:
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   base::ScopedTempDir temp_dir_;
 };