Cancel previous scan when replacing the directory contents.

BUG=138703
TEST=Changing search string or directory while previous search or directory scan is still running.

Review URL: https://chromiumcodereview.appspot.com/10828051

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148940 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/resources/file_manager/js/directory_model.js

@@ -387,6 +387,7 @@ DirectoryModel.prototype.rescan = function() {
  */
 DirectoryModel.prototype.clearAndScan_ = function(newDirContents,
                                                   opt_callback) {
+  this.currentDirContents_.cancelScan();
   this.currentDirContents_ = newDirContents;
   this.clearRescanTimeout_();