Fix type annotation to pass the closure compiler.

ui/file_manager/file_manager/foreground/js/metadata/metadata_cache.js

 // Copyright (c) 2012 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.
 
 /**
  * MetadataCache is a map from Entry to an object containing properties.
  * Properties are divided by types, and all properties of one type are accessed
  * at once.
  * Some of the properties:
  * {
@@ skipping 111 matching lines @@
     new ExternalProvider(volumeManager),
     new FilesystemProvider(),
     new ContentProvider()
   ]);
 };
 
 /**
  * Clones metadata entry. Metadata entries may contain scalars, arrays,
  * hash arrays and Date object. Other objects are not supported.
  * @param {Object} metadata Metadata object.
- * @return {!Object} Cloned entry.
+ * @return {Object} Cloned entry.
  */
 MetadataCache.cloneMetadata = function(metadata) {
   if (metadata instanceof Array) {
     var result = [];
     for (var index = 0; index < metadata.length; index++) {
       result[index] = MetadataCache.cloneMetadata(metadata[index]);
     }
     return result;
   } else if (metadata instanceof Date) {
     var result = new Date();
@@ skipping 966 matching lines @@
 
 /**
  * Handles the 'log' message from the worker.
  * @param {Array.<*>} arglist Log arguments.
  * @private
  */
 ContentProvider.prototype.onLog_ = function(arglist) {
   if (MetadataCache.log)  // Avoid log spam by default.
     console.log.apply(console, ['metadata:'].concat(arglist));
 };