Move content deduplication into the scan process.

ui/file_manager/file_manager/background/js/mock_media_scanner.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.
 
 /**
  * importer.MediaScanner and importer.ScanResult test double.
  *
  * @constructor
  * @struct
  * @implements {importer.MediaScanner}
@@ skipping 97 matching lines @@
    * @type {!Array.<!FileEntry>}
    */
   this.fileEntries = fileEntries.slice();
 
   /** @type {number} */
   this.totalBytes = 100;
 
   /** @type {number} */
   this.scanDuration = 100;
 
-  /** @type {number} */
-  this.duplicateFileCount = 0;
-
   /** @type {function} */
   this.resolveResult_;
 
   /** @type {function} */
   this.rejectResult_;
 
   /** @type {boolean} */
   this.settled_ = false;
 
   /** @type {!Promise.<!importer.ScanResult>} */
@@ skipping 33 matching lines @@
 /** @override */
 TestScanResult.prototype.isInvalidated = function() {
   return false;
 };
 
 /** @override */
 TestScanResult.prototype.getStatistics = function() {
   return {
     scanDuration: this.scanDuration,
     newFileCount: this.fileEntries.length,
-    duplicateFileCount: this.duplicateFileCount,
+    duplicates: {},
     sizeBytes: this.totalBytes
   };
 };
 
 /**
  * @constructor
  * @implements {importer.DirectoryWatcher}
  */
 function TestDirectoryWatcher(callback) {
   /**
    * @public {function()}
    * @const
    */
   this.callback = callback;
 
   /**
    * @public {boolean}
    */
   this.triggered = false;
 };
 
 /**
  * @override
  */
 TestDirectoryWatcher.prototype.addDirectory = function() {
 };