Files.app: Show thumbnail of non-image file even when the file cache is present

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.
 
 'use strict';
 
 /**
  * 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.
@@ skipping 855 matching lines @@
     pinned: data.isPinned,
     hosted: data.isHosted,
     imageWidth: data.imageWidth,
     imageHeight: data.imageHeight,
     imageRotation: data.imageRotation,
     availableOffline: data.isAvailableOffline,
     availableWhenMetered: data.isAvailableWhenMetered,
     customIconUrl: data.customIconUrl || '',
     contentMimeType: data.contentMimeType || '',
     sharedWithMe: data.sharedWithMe,
-    shared: data.shared
+    shared: data.shared,
+    thumbnailUrl: data.thumbnailUrl  // Thumbnail passed from external server.

[mtomasz, 2014/09/17 09:29:48]

ExternalProvider used to provide a thumbnail field if the file is not cached.
See #804. However, after this change it's not. Calling
metadataCache.get([entry], 'thumbnail') would skip the ExternalProvider and
cause downloading the entire file to get a thumbnail from file if it's not
cached, what may kill performance of the grid view and mosaic view.

[yoshiki, 2014/09/17 09:57:09]

I got it. I add the code to fill thumbnail field when the file is present below.

   };
 
   result.filesystem = {
     size: (entry.isFile ? (data.fileSize || 0) : -1),
     modificationTime: new Date(data.lastModifiedTime)
   };
 
-  if ('thumbnailUrl' in data) {
-    result.thumbnail = {
-      url: data.thumbnailUrl,
-      transform: null
-    };
-  } else if (data.isPresent) {
-    result.thumbnail = null;
-  } else {
-    // Not present in cache, so do not allow to generate it by next providers.
-    result.thumbnail = {url: '', transform: null};
-  }
-
   // If present in cache, then allow to fetch media by next providers.
   result.media = data.isPresent ? null : {};
 
   return result;
 };
 
 
 /**
  * Provider of content metadata.
  * This provider returns the following objects:
@@ skipping 180 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));
 };