Add background-wide file metadata cache.

ui/file_manager/file_manager/background/js/file_operation_manager.js

Index: ui/file_manager/file_manager/background/js/file_operation_manager.js
diff --git a/ui/file_manager/file_manager/background/js/file_operation_manager.js b/ui/file_manager/file_manager/background/js/file_operation_manager.js
index 8400b96bec8ed606232781b16ed6e7f83a6d7e9f..f73e384ccc29aa3fec03adbdda12912ae445c63a 100644
--- a/ui/file_manager/file_manager/background/js/file_operation_manager.js
+++ b/ui/file_manager/file_manager/background/js/file_operation_manager.js
@@ -370,16 +370,18 @@ FileOperationManager.prototype.deleteEntries = function(entries) {
   var group = new AsyncUtil.Group();
   for (var i = 0; i < task.entries.length; i++) {
     group.add(function(entry, callback) {
-      entry.getMetadata(function(metadata) {
-        task.entrySize[entry.toURL()] = metadata.size;
-        task.totalBytes += metadata.size;
-        callback();
-      }, function() {
-        // Fail to obtain the metadata. Use fake value 1.
-        task.entrySize[entry.toURL()] = 1;
-        task.totalBytes += 1;
-        callback();
-      });
+      metadataProxy.getEntryMetadata(entry).then(
+          function(metadata) {
+            task.entrySize[entry.toURL()] = metadata.size;
+            task.totalBytes += metadata.size;
+            callback();
+          },
+          function() {
+            // Fail to obtain the metadata. Use fake value 1.
+            task.entrySize[entry.toURL()] = 1;
+            task.totalBytes += 1;
+            callback();
+          });
     }.bind(this, task.entries[i]));
   }