[Mac] Reduce jank in the cookie manager by lazily creating child nodes for the UI.

chrome/browser/cocoa/cookies_window_controller.mm

 // Copyright (c) 2010 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/cocoa/cookies_window_controller.h"
 
 #include <vector>
 
 #include "app/l10n_util_mac.h"
 #include "app/resource_bundle.h"
@@ skipping 288 matching lines @@
   if ([children count] == 1U) {
     // The node that will expand has one child. Do the user a favor and expand
     // that node (saving her a click) if it is non-leaf.
     CocoaCookieTreeNode* child = [children lastObject];
     if (![child isLeaf]) {
       NSOutlineView* outlineView = [notif object];
       // Tell the OutlineView to expand the NSTreeNode, not the model object.
       children = [item childNodes];
       DCHECK_EQ([children count], 1U);
       [outlineView expandItem:[children lastObject]];
+      // Select the first node in that child set.
+      NSTreeNode* folderChild = [children lastObject];
+      if ([[folderChild childNodes] count] > 0) {        
+        NSTreeNode* firstCookieChild =
+            [[folderChild childNodes] objectAtIndex:0];
+        [treeController_ setSelectionIndexPath:[firstCookieChild indexPath]];
+      }
     }
   }
 }
 
 - (void)outlineViewSelectionDidChange:(NSNotification*)notif {
   // Multi-selection should be disabled in the UI, but for sanity, double-check
   // that they can't do it here.
   NSUInteger count = [[treeController_ selectedObjects] count];
   if (count != 1U) {
     DCHECK_LT(count, 1U) << "User was able to select more than 1 cookie node!";
@@ skipping 52 matching lines @@
   [icons_ addObject:rb.GetNSImageNamed(IDR_BOOKMARK_BAR_FOLDER)];
 
   // Create the Cocoa model.
   CookieTreeNode* root = static_cast<CookieTreeNode*>(treeModel_->GetRoot());
   scoped_nsobject<CocoaCookieTreeNode> model(
       [[CocoaCookieTreeNode alloc] initWithNode:root]);
   [self setCocoaTreeModel:model.get()];  // Takes ownership.
 }
 
 @end