Files.app: Fix DirectoryModel#partialUpdate so that it does not ignore changes.

Previously DirectoryModel#partialUpdate ignores changes if the function is
called multiple times during the previous request is being procecced.

BUG=417163
TEST=Repo steps of the bug.

Review URL: https://codereview.chromium.org/611193002

Cr-Commit-Position: refs/heads/master@{#297381}

ui/file_manager/file_manager/foreground/js/directory_model.js

@@ -468,8 +468,7 @@ DirectoryModel.prototype.partialUpdate_ =
                                        onPreviousScanCompleted);
       // Run the update asynchronously.
       Promise.resolve().then(function() {
-        if (!this.runningScan_)
-          this.partialUpdate_(changedEntries, removedUrls);
+        this.partialUpdate_(changedEntries, removedUrls);
       }.bind(this));
     }.bind(this);
     previousScan.addEventListener('scan-completed', onPreviousScanCompleted);