gin test - add simple file access for JS

gin/test/file_unittests.js

+// 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.
+
+define([
+    "gin/test/expect",
+    "file"
+  ], function(expect, file) {
+
+  function isString(x) {
+    return toString.call(x) === '[object String]'
+  }
+
+  var rootDir = file.getSourceRootDirectory();
+  expect(isString(rootDir)).toBeTruthy();
+
+  var noArgsNull = file.getFilesInDirectory();
+  expect(noArgsNull).toBeNull();
+
+  var files = file.getFilesInDirectory(rootDir);
+  expect(Array.isArray(files)).toBeTruthy();
+
+  var nsdNull = file.getFilesInDirectory(rootDir + "/no_such_dir");
+  expect(nsdNull).toBeNull();
+
+  var owners = file.readFileToString(rootDir + "/OWNERS");
+  expect(isString(owners)).toBeTruthy();
+  expect(owners.length).toBeGreaterThan(0);
+
+  noArgsNull = file.readFileToString();
+  expect(noArgsNull).toBeNull();
+
+  var nsfNull = file.readFileToString(rootDir + "/no_such_file");
+  expect(nsfNull).toBeNull();
+
+  this.result = "PASS";
+});