Files.app: Show error messages for the case the source file is not exists.

chrome/browser/resources/file_manager/foreground/js/file_transfer_controller.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';
 
 /**
  * Global (placed in the window object) variable name to hold internal
  * file dragging information. Needed to show visual feedback while dragging
  * since DataTransfer object is in protected state. Reachable from other
@@ skipping 222 matching lines @@
    * @param {DataTransfer} dataTransfer System data transfer object.
    * @param {DirectoryEntry=} opt_destinationEntry Paste destination.
    * @param {string=} opt_effect Desired drop/paste effect. Could be
    *     'move'|'copy' (default is copy). Ignored if conflicts with
    *     |dataTransfer.effectAllowed|.
    * @return {string} Either "copy" or "move".
    */
   paste: function(dataTransfer, opt_destinationEntry, opt_effect) {
     var sourceURLs = dataTransfer.getData('fs/sources') ?
         dataTransfer.getData('fs/sources').split('\n') : [];
-    util.URLsToEntries(sourceURLs, function(sourceEntries) {
-      var destinationEntry =
-          opt_destinationEntry || this.currentDirectoryContentEntry;
-      // Start the pasting operation.
-      this.fileOperationManager_.paste(sourceEntries, destinationEntry, toMove);
-    }.bind(this));
-
     // effectAllowed set in copy/paste handlers stay uninitialized. DnD handlers
     // work fine.
     var effectAllowed = dataTransfer.effectAllowed !== 'uninitialized' ?
         dataTransfer.effectAllowed : dataTransfer.getData('fs/effectallowed');
     var toMove = effectAllowed === 'move' ||
         (effectAllowed === 'copyMove' && opt_effect === 'move');
 
+    util.URLsToEntries(sourceURLs, function(sourceEntries, failureUrls) {
+      var destinationEntry =
+          opt_destinationEntry || this.currentDirectoryContentEntry;
+      // Start the pasting operation.
+      this.fileOperationManager_.paste(sourceEntries, destinationEntry, toMove);
+
+      // Publish events for failureUrls.
+      for (var i = 0; i < failureUrls.length; i++) {
+        var fileName = decodeURIComponent(failureUrls[i].replace(/^.+\//, ''));
+        var event = new Event('source-not-found');
+        event.fileName = fileName;
+        event.progressType =
+            toMove ? ProgressItemType.MOVE : ProgressItemType.COPY;
+        this.dispatchEvent(event);
+      }
+    }.bind(this));
     return toMove ? 'move' : 'copy';
   },
 
   /**
    * Preloads an image thumbnail for the specified file entry.
    *
    * @this {FileTransferController}
    * @param {Entry} entry Entry to preload a thumbnail for.
    */
   preloadThumbnailImage_: function(entry) {
@@ skipping 658 matching lines @@
         !event.ctrlKey) {
       return 'move';
     }
     if (event.dataTransfer.effectAllowed === 'copyMove' &&
         event.shiftKey) {
       return 'move';
     }
     return 'copy';
   },
 };