Fix crash in DirectoryImpl::Flush()

components/filesystem/directory_impl_unittest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
 #include <string>
 
@@ skipping 258 matching lines @@
 
   {
     std::string data("one two three");
     bool handled = directory->WriteFile(
         "my_dir", mojo::Array<uint8_t>::From(data), &error);
     ASSERT_TRUE(handled);
     EXPECT_EQ(mojom::FileError::NOT_A_FILE, error);
   }
 }
 
+TEST_F(DirectoryImplTest, Flush) {
+  mojom::DirectoryPtr directory;
+  GetTemporaryRoot(&directory);
+  mojom::FileError error;
+
+  {
+    bool handled = directory->Flush(&error);
+    ASSERT_TRUE(handled);
+    EXPECT_EQ(mojom::FileError::OK, error);
+  }
+}
+
 // TODO(vtl): Test delete flags.
 
 }  // namespace
 }  // namespace filesystem