Add MetadataCacheSetStorage implementation for LRUCache.

ui/file_manager/file_manager/foreground/js/metadata/metadata_cache_set.js

Index: ui/file_manager/file_manager/foreground/js/metadata/metadata_cache_set.js
diff --git a/ui/file_manager/file_manager/foreground/js/metadata/metadata_cache_set.js b/ui/file_manager/file_manager/foreground/js/metadata/metadata_cache_set.js
index 9fc872f7a9b4baf44dcbf468ef4d0441d7956a3b..15f4693999b83e94fd74f92efe89d79f14d250c7 100644
--- a/ui/file_manager/file_manager/foreground/js/metadata/metadata_cache_set.js
+++ b/ui/file_manager/file_manager/foreground/js/metadata/metadata_cache_set.js
@@ -134,7 +134,6 @@ MetadataCacheSet.prototype.hasFreshCache = function(entries, names) {
 
 /**
  * Interface of raw strage for MetadataCacheItem.
- * TODO(hirono): Add implementation of the interface for LRUCache.
  * @interface
  */
 function MetadataCacheSetStorage() {
@@ -173,19 +172,64 @@ function MetadataCacheSetStorageForObject(items) {
   this.items_ = items;
 }
 
+/**
+ * @override
+ */
 MetadataCacheSetStorageForObject.prototype.get = function(url) {
   return this.items_[url];
 };
 
+/**
+ * @override
+ */
 MetadataCacheSetStorageForObject.prototype.peek = function(url) {
   return this.items_[url];
 };
 
+/**
+ * @override
+ */
 MetadataCacheSetStorageForObject.prototype.put = function(url, item) {
   this.items_[url] = item;
 };
 
 /**
+ * Implementation of MetadataCacheSetStorage by using LRUCache.
+ * @param {!LRUCache<!MetadataCacheItem>} cache LRUCache.
+ * @constructor
+ * @implements {MetadataCacheSetStorage}
+ * @struct
+ */
+function MetadataCacheSetStorageForLRUCache(cache) {
+  /**
+   * @private {!LRUCache<!MetadataCacheItem>}
+   * @const
+   */
+  this.cache_ = cache;
+}
+
+/**
+ * @override
+ */
+MetadataCacheSetStorageForLRUCache.prototype.get = function(url) {
+  return this.cache_.get(url);
+};
+
+/**
+ * @override
+ */
+MetadataCacheSetStorageForLRUCache.prototype.peek = function(url) {
+  return this.cache_.peek(url);
+};
+
+/**
+ * @override
+ */
+MetadataCacheSetStorageForLRUCache.prototype.put = function(url, item) {
+  this.cache_.put(url, item);
+};
+
+/**
  * @param {!FileEntry} entry Entry
  * @param {!Array<string>} names Property name list to be requested.
  * @constructor