ui/base/models: Add empty() accessor to TreeNode class.

chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.mm

 // Copyright (c) 2011 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.
 
 #import "chrome/browser/ui/cocoa/bookmarks/bookmark_bar_controller.h"
 
 #include "app/mac/nsimage_cache.h"
 #include "base/mac/mac_util.h"
 #include "base/metrics/histogram.h"
 #include "base/sys_string_conversions.h"
@@ skipping 1190 matching lines @@
   const BookmarkNode* node = bookmarkModel_->GetNodeByID(tag);
   WindowOpenDisposition disposition =
       event_utils::WindowOpenDispositionFromNSEvent([NSApp currentEvent]);
   [self openURL:node->GetURL() disposition:disposition];
 }
 
 // For the given root node of the bookmark bar, show or hide (as
 // appropriate) the "no items" container (text which says "bookmarks
 // go here").
 - (void)showOrHideNoItemContainerForNode:(const BookmarkNode*)node {
-  BOOL hideNoItemWarning = node->child_count() > 0;
+  BOOL hideNoItemWarning = !node->empty();
   [[buttonView_ noItemContainer] setHidden:hideNoItemWarning];
 }
 
 // TODO(jrg): write a "build bar" so there is a nice spot for things
 // like the contextual menu which is invoked when not over a
 // bookmark.  On Safari that menu has a "new folder" option.
 - (void)addNodesToButtonList:(const BookmarkNode*)node {
   [self showOrHideNoItemContainerForNode:node];
 
   CGFloat maxViewX = NSMaxX([[self view] bounds]);
@@ skipping 1500 matching lines @@
 // to minimize touching the object passed in (likely a mock).
 - (void)setButtonContextMenu:(id)menu {
   buttonContextMenu_ = menu;
 }
 
 - (void)setIgnoreAnimations:(BOOL)ignore {
   ignoreAnimations_ = ignore;
 }
 
 @end