Remove watchers spam from log.

ui/file_manager/file_manager/foreground/js/directory_model.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.
 
 // If directory files changes too often, don't rescan directory more than once
 // per specified interval
 var SIMULTANEOUS_RESCAN_INTERVAL = 500;
 // Used for operations that require almost instant rescan.
 var SHORT_RESCAN_INTERVAL = 100;
 
@@ skipping 927 matching lines @@
     dirEntry, opt_callback) {
   // Increment the sequence value.
   this.changeDirectorySequence_++;
   this.clearSearch_();
 
   // If there is on-going scan, cancel it.
   if (this.currentDirContents_.isScanning())
     this.currentDirContents_.cancelScan();
 
   this.directoryChangeQueue_.run(function(sequence, queueTaskCallback) {
-    this.fileWatcher_.changeWatchedDirectory(
-        dirEntry,
-        function() {
+    this.fileWatcher_.changeWatchedDirectory(dirEntry)
+        .then(function() {
           if (this.changeDirectorySequence_ !== sequence) {
             queueTaskCallback();
             return;
           }
 
           var newDirectoryContents = this.createDirectoryContents_(
               this.currentFileListContext_, dirEntry, '');
           if (!newDirectoryContents) {
             queueTaskCallback();
             return;
@@ skipping 352 matching lines @@
   if (this.onSearchCompleted_) {
     this.removeEventListener('scan-completed', this.onSearchCompleted_);
     this.onSearchCompleted_ = null;
   }
 
   if (this.onClearSearch_) {
     this.onClearSearch_();
     this.onClearSearch_ = null;
   }
 };