[filebrowser] More reliable file saving in Photo Editor

chrome/browser/resources/file_manager/js/image_editor/image_encoder.js

 // Copyright (c) 2011 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.
 
 /**
  * A namespace class for image encoding functions. All methods are static.
  */
 function ImageEncoder() {}
 
 ImageEncoder.MAX_THUMBNAIL_DIMENSION = 320;
@@ skipping 139 matching lines @@
 /**
  * A base class for a metadata encoder.
  *
  * Serves as a default metadata encoder for images that none of the metadata
  * parsers recognized.
  *
  * @param {Object} original_metadata
  */
 ImageEncoder.MetadataEncoder = function(original_metadata) {
   this.metadata_ = ImageUtil.deepCopy(original_metadata) || {};
-  if (!this.metadata_.mimeType) {
-    // For the purposes saving to a file and thumbnail generation we assume
-    // it is a png.
+  if (this.metadata_.mimeType != 'image/jpeg') {
+    // Chrome can only encode JPEG and PNG. Force PNG mime type so that we
+    // can save to file and generate a thumbnail.
     this.metadata_.mimeType = 'image/png';
   }
 };
 
 ImageEncoder.MetadataEncoder.prototype.getMetadata = function() {
   return this.metadata_;
 };
 
 /**
  * @param {HTMLCanvasElement|Object} canvas Canvas or or anything with
@@ skipping 23 matching lines @@
     findInsertionRange = function(encodedImage) { return {from: 0, to: 0} };
 
 /**
  * Return serialized metadata ready to write to an image file.
  * The return type is optimized for passing to Blob.append.
  * @return {ArrayBuffer}
  */
 ImageEncoder.MetadataEncoder.prototype.encode = function() {
   return new Uint8Array(0).buffer;
 };