Simplify volume manager in Files app.

chrome/test/data/file_manager/unit_tests/mocks/mock_file_system.js

Index: chrome/test/data/file_manager/unit_tests/mocks/mock_file_system.js
diff --git a/chrome/test/data/file_manager/unit_tests/mocks/mock_file_system.js b/chrome/test/data/file_manager/unit_tests/mocks/mock_file_system.js
new file mode 100644
index 0000000000000000000000000000000000000000..58c4e23db0c1c2f64089cdb10571510dd81959ff
--- /dev/null
+++ b/chrome/test/data/file_manager/unit_tests/mocks/mock_file_system.js
@@ -0,0 +1,13 @@
+// Copyright 2014 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.
+
+/**
+ * Mock class for DOMFileSystem.
+ * @param {string} volumeId Volume ID for the file system.
+ * @constructor
+ */
+function MockFileSystem(volumeId) {
+  this.name = '';
+  this.root = new MockFileEntry(volumeId, '/');
+}