[MD Bookmarks] Prevent sorting of empty folders.

chrome/test/data/webui/md_bookmarks/toolbar_test.js

Index: chrome/test/data/webui/md_bookmarks/toolbar_test.js
diff --git a/chrome/test/data/webui/md_bookmarks/toolbar_test.js b/chrome/test/data/webui/md_bookmarks/toolbar_test.js
index f01fcf6d90dbe7d02345fb3e682353a476abf0d0..d56cba5f012042f26ddfb1d7e74f2d89ed450b2b 100644
--- a/chrome/test/data/webui/md_bookmarks/toolbar_test.js
+++ b/chrome/test/data/webui/md_bookmarks/toolbar_test.js
@@ -19,6 +19,12 @@ suite('<bookmarks-toolbar>', function() {
             createItem('2'),
             createItem('3'),
             createFolder('4', [], {unmodifiable: 'managed'}),
+            createFolder('5', []),
+            createFolder(
+                '6',
+                [
+                  createItem('61'),
+                ]),
           ])),
       selection: {
         items: new Set(),
@@ -108,4 +114,20 @@ suite('<bookmarks-toolbar>', function() {
     assertTrue(toolbar.$$('#addBookmarkButton').disabled);
     assertTrue(toolbar.$$('#importBookmarkButton').disabled);
   });
+
+  test('sort button is disabled when folder is empty', function() {
+    MockInteractions.tap(toolbar.$.menuButton);
+
+    store.data.selectedFolder = '6';
+    store.notifyObservers();
+    Polymer.dom.flush();

[tsergeant, 2017/07/10 07:09:08]

Nit: Are these flushes actually necessary? I wouldn't really expect them to be,
so remove them if you can.

[calamity, 2017/07/11 06:53:10]

Done.

+    assertTrue(toolbar.canSortFolder_);
+
+    store.data.selectedFolder = '5';
+    store.notifyObservers();
+    Polymer.dom.flush();
+
+    assertFalse(toolbar.canSortFolder_);
+    assertTrue(toolbar.$$('#sortButton').disabled);
+  });
 });