Use ScopedTaskEnvironment instead of MessageLoop in content unit tests.

content/browser/fileapi/transient_file_util_unittest.cc

Index: content/browser/fileapi/transient_file_util_unittest.cc
diff --git a/content/browser/fileapi/transient_file_util_unittest.cc b/content/browser/fileapi/transient_file_util_unittest.cc
index 8b747e5e0876b25fb7ff6ca48caf72992d0f2a36..8104045dd284bcee99a5e2a6742e6c3cc7165360 100644
--- a/content/browser/fileapi/transient_file_util_unittest.cc
+++ b/content/browser/fileapi/transient_file_util_unittest.cc
@@ -10,6 +10,7 @@
 #include "base/macros.h"
 #include "base/memory/ptr_util.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "content/public/test/test_file_system_context.h"
 #include "storage/browser/blob/scoped_file.h"
 #include "storage/browser/fileapi/file_system_context.h"
@@ -69,7 +70,7 @@ class TransientFileUtilTest : public testing::Test {
   }
 
  private:
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   base::ScopedTempDir data_dir_;
   scoped_refptr<storage::FileSystemContext> file_system_context_;
   std::unique_ptr<storage::TransientFileUtil> transient_file_util_;