Do not call stat() when reading directories via File API.

chrome/common/extensions/api/file_system_provider.idl

 // Copyright 2013 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.
 
 // Use the <code>chrome.fileSystemProvider</code> API to create file systems,
 // that can be accessible from the file manager on Chrome OS.
 [implemented_in="chrome/browser/chromeos/extensions/file_system_provider/file_system_provider_api.h"]
 namespace fileSystemProvider {
   // Error codes used by providing extensions in response to requests as well
   // as in case of errors when calling methods of the API. For success,
@@ skipping 43 matching lines @@
 
   // Represents metadata of a file or a directory.
   dictionary EntryMetadata {
     // True if it is a directory.
     boolean isDirectory;
 
     // Name of this entry (not full path name). Must not contain '/'. For root
     // it must be empty.
     DOMString name;
 
-    // File size in bytes.
-    double size;
+    // File size in bytes. Required for <code>OnGetMetadataRequested</code>.
+    double? size;
 
-    // The last modified time of this entry.
-    [instanceOf=Date] object modificationTime;
+    // The last modified time of this entry. Required for
+    // <code>OnGetMetadataRequested</code>.
+    [instanceOf=Date] object? modificationTime;
 
     // Mime type for the entry.
     DOMString? mimeType;
 
     // Thumbnail image as a data URI in either PNG, JPEG or WEBP format, at most
     // 32 KB in size. Optional, but can be provided only when explicitly
     // requested by the $(ref:onGetMetadataRequested) event.
     DOMString? thumbnail;
   };
 
@@ skipping 656 matching lines @@
     // Raised when executing an action for a set of files or directories is\
     // requested. After the action is completed, <code>successCallback</code>
     // must be called. On error, <code>errorCallback</code> must be called.
     [maxListeners=1, nodoc] static void onExecuteActionRequested(
       ExecuteActionRequestedOptions options,
       ProviderSuccessCallback successCallback,
       ProviderErrorCallback errorCallback);
   };
 };