[MD Bookmarks] Make folder nodes extend their whole width.

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

 // Copyright 2016 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.
 
 suite('<bookmarks-sidebar>', function() {
   var sidebar;
   var store;
 
   setup(function() {
     store = new bookmarks.TestStore({
@@ skipping 13 matching lines @@
       ])),
     });
     bookmarks.Store.instance_ = store;
 
     sidebar = document.createElement('bookmarks-sidebar');
     replaceBody(sidebar);
     Polymer.dom.flush();
   });
 
   test('selecting and deselecting folders dispatches action', function() {
-    var rootFolders = sidebar.$['folder-tree'].children;
+    var rootFolders =
+        sidebar.$['folder-tree'].querySelectorAll('bookmarks-folder-node');
     var firstGen = rootFolders[0].$['descendants'].querySelectorAll(
         'bookmarks-folder-node');
     var secondGen =
         firstGen[0].$['descendants'].querySelectorAll('bookmarks-folder-node');
 
     // Select nested folder.
     firedId = '';
     MockInteractions.tap(secondGen[0].$['folder-label']);
     assertEquals('select-folder', store.lastAction.name);
     assertEquals(secondGen[0].itemId, store.lastAction.id);
 
     // Select folder in a separate subtree.
     firedId = '';
     MockInteractions.tap(rootFolders[1].$['folder-label']);
     assertEquals('select-folder', store.lastAction.name);
     assertEquals(rootFolders[1].itemId, store.lastAction.id);
   });
+
+  test('depth calculation', function() {
+    var rootFolders =
+        sidebar.$['folder-tree'].querySelectorAll('bookmarks-folder-node');
+    var firstGen = rootFolders[0].$['descendants'].querySelectorAll(
+        'bookmarks-folder-node');
+    var secondGen =
+        firstGen[0].$['descendants'].querySelectorAll('bookmarks-folder-node');
+
+    Array.prototype.forEach.call(rootFolders, function(f) {
+      assertEquals(0, f.depth);
+      assertEquals('0', f.style.getPropertyValue('--node-depth'));
+    });
+    Array.prototype.forEach.call(firstGen, function(f) {
+      assertEquals(1, f.depth);
+      assertEquals('1', f.style.getPropertyValue('--node-depth'));
+    });
+    Array.prototype.forEach.call(secondGen, function(f) {
+      assertEquals(2, f.depth);
+      assertEquals('2', f.style.getPropertyValue('--node-depth'));
+    });
+  })
 });