Add a subtle reminder that chrome_extensions.js is overwritten.

ui/file_manager/image_loader/image_loader.js

 // 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.
 
 /**
  * Loads and resizes an image.
  * @constructor
  */
 function ImageLoader() {
   /**
@@ skipping 24 matching lines @@
         function(event) {
           if (event.eventType === 'mount' && event.status === 'success') {
             chrome.fileSystem.requestFileSystem(
                 {volumeId: event.volumeMetadata.volumeId}, function() {});
           }
         });
     var initPromises = volumeMetadataList.map(function(volumeMetadata) {
       var requestPromise = new Promise(function(callback) {
         chrome.fileSystem.requestFileSystem(
             {volumeId: volumeMetadata.volumeId},
-            callback);
+            /** @type {function(FileSystem=)} */(callback));
       });
       return requestPromise;
     });
     initPromises.push(new Promise(function(resolve, reject) {
       this.cache_.initialize(resolve);
     }.bind(this)));
 
     // After all initialization promises are done, start the scheduler.
     Promise.all(initPromises).then(this.scheduler_.start.bind(this.scheduler_));
   }.bind(this));
@@ skipping 164 matching lines @@
   var targetContext = target.getContext('2d');
   targetContext.save();
   orientation.cancelImageOrientation(
       targetContext, targetDimensions.width, targetDimensions.height);
   targetContext.drawImage(
       source,
       0, 0, source.width, source.height,
       0, 0, targetDimensions.width, targetDimensions.height);
   targetContext.restore();
 };