Files.app: Add a deduplication step to avoid importing duplicate media.

ui/file_manager/file_manager/common/js/importer_common.js

 // Copyright 2014 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.
 
 // Shared cloud importer namespace
 var importer = importer || {};
 
 /** @enum {string} */
 importer.ScanEvent = {
   FINALIZED: 'finalized',
@@ skipping 560 matching lines @@
        */
       function(resolve, reject) {
         writer.onwriteend = resolve;
         writer.onerror = reject;
 
         writer.seek(writer.length);
         writer.write(blob);
       }.bind(this));
 };
 
-/** @type {importer.Logger} */
+/** @private {importer.Logger} */
 importer.logger_ = null;
 
 /**
  * Creates a new logger instance...all ready to go.
  *
  * @return {!importer.Logger}
  */
 importer.getLogger = function() {
   if (!importer.logger_) {
     importer.logger_ = new importer.RuntimeLogger(
         importer.ChromeSyncFileEntryProvider.getFileEntry(
             'importer_debug.log'));
   }
   return importer.logger_;
 };