Use ScopedTaskEnvironment instead of MessageLoop in storage unit tests.

storage/browser/fileapi/quota/quota_backend_impl_unittest.cc

Index: storage/browser/fileapi/quota/quota_backend_impl_unittest.cc
diff --git a/storage/browser/fileapi/quota/quota_backend_impl_unittest.cc b/storage/browser/fileapi/quota/quota_backend_impl_unittest.cc
index ea45863b3912ef09c14c063da6eb1c03f111aa03..78e05df0c30819cd38f435310b3540f5510c804b 100644
--- a/storage/browser/fileapi/quota/quota_backend_impl_unittest.cc
+++ b/storage/browser/fileapi/quota/quota_backend_impl_unittest.cc
@@ -12,6 +12,7 @@
 #include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
 #include "base/run_loop.h"
+#include "base/test/scoped_task_environment.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "storage/browser/fileapi/file_system_usage_cache.h"
 #include "storage/browser/fileapi/obfuscated_file_util.h"
@@ -146,7 +147,7 @@ class QuotaBackendImplTest : public testing::Test {
     return path;
   }
 
-  base::MessageLoop message_loop_;
+  base::test::ScopedTaskEnvironment scoped_task_environment_;
   base::ScopedTempDir data_dir_;
   std::unique_ptr<leveldb::Env> in_memory_env_;
   std::unique_ptr<ObfuscatedFileUtil> file_util_;