Use ScopedTaskEnvironment instead of MessageLoop in content unit tests.

content/browser/fileapi/copy_or_move_file_validator_unittest.cc

Index: content/browser/fileapi/copy_or_move_file_validator_unittest.cc
diff --git a/content/browser/fileapi/copy_or_move_file_validator_unittest.cc b/content/browser/fileapi/copy_or_move_file_validator_unittest.cc
index 5efd37bae2802e2a7ac21d975cd4d18fa74166c1..ce496b10b2d88ee3fb58fab7b0ed032d1b8281e0 100644
--- a/content/browser/fileapi/copy_or_move_file_validator_unittest.cc
+++ b/content/browser/fileapi/copy_or_move_file_validator_unittest.cc
@@ -13,6 +13,7 @@
 #include "base/macros.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "content/public/test/async_file_test_helper.h"
 #include "content/public/test/mock_special_storage_policy.h"
@@ -179,7 +180,7 @@ class CopyOrMoveFileValidatorTestHelper {
   std::string src_fsid_;
   std::string dest_fsid_;
 
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   scoped_refptr<storage::FileSystemContext> file_system_context_;
 
   FileSystemURL copy_src_;