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

chrome/browser/cocoa/cookie_tree_node.h

Index: chrome/browser/cocoa/cookie_tree_node.h
diff --git a/chrome/browser/cocoa/cookie_tree_node.h b/chrome/browser/cocoa/cookie_tree_node.h
index 5ff66958a3fc5fde366cddf51ae51ddcc872a806..1f161d54c699bd1a6605711facd3f8e26e6ea791 100644
--- a/chrome/browser/cocoa/cookie_tree_node.h
+++ b/chrome/browser/cocoa/cookie_tree_node.h
@@ -12,6 +12,8 @@
 @interface CocoaCookieTreeNode : NSObject {
   scoped_nsobject<NSString> title_;
   scoped_nsobject<NSMutableArray> children_;
+  // We lazily create children, so we need to know if we are a leaf.
+  BOOL isLeaf_;
 
   // The platform-independent model node.
   CookieTreeNode* treeNode_;  // weak
@@ -39,7 +41,7 @@
 // Getters.
 - (NSString*)title;
 // |-children| is mutable so that the CookiesTreeModelObserverBridge can
-// operate on the children.
+// operate on the children. Note that this lazily creates children.
 - (NSMutableArray*)children;
 - (TreeModelNode*)treeNode;