Quick View: fixed the bug that 'No preview available' text is not shown.

ui/file_manager/file_manager/foreground/elements/files_quick_view.js

 // Copyright 2016 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.
 
 var FilesQuickView = Polymer({
   is: 'files-quick-view',
 
   properties: {
     // File media type, e.g. image, video.
     type: String,
     filePath: String,
     // URLs should be accessible from webview since contets are rendered inside
     // it. Hint: use URL.createObjectURL.
     contentUrl: String,
     videoPoster: String,
     audioArtwork: String,
     autoplay: Boolean,
 
     // metadata-box-active-changed event is fired on attribute change.
     metadataBoxActive: {
       value: true,
       type: Boolean,
       notify: true,
-    }
+    },
+    // Text shown when no playback is available.
+    noPlaybackText: String,
+    // Text shown when no preview is available.
+    noPreviewText: String,
   },
 
   listeners: {
     'iron-overlay-closed': 'clear',
     'files-safe-media-tap-outside': 'close',
   },
 
   // Clears fields.
   clear: function() {
     this.type = '';
@@ skipping 115 matching lines @@
    * @param {string} type
    * @return {boolean}
    *
    * @private
    */
   isUnsupported_: function(type) {
     return !this.isImage_(type) && !this.isVideo_(type) && !this.isAudio_(type);
   },
 
 });