Only commit cookie changes in prerenders after a prerender is shown

net/cookies/canonical_cookie.h

Index: net/cookies/canonical_cookie.h
===================================================================
--- net/cookies/canonical_cookie.h	(revision 269781)
+++ net/cookies/canonical_cookie.h	(working copy)
@@ -125,6 +125,9 @@
 
   std::string DebugString() const;
 
+  // Returns a duplicate of this cookie.
+  CanonicalCookie* Duplicate();
+
   // Returns the cookie source when cookies are set for |url|. This function
   // is public for unit test purposes only.
   static std::string GetCookieSourceFromURL(const GURL& url);
@@ -134,6 +137,9 @@
                                     const base::Time& server_time);
 
  private:
+  // NOTE: When any new members are added below, the implementation of
+  // Duplicate() must be updated to copy the new member accordingly.
+
   // The source member of a canonical cookie is the origin of the URL that tried
   // to set this cookie, minus the port number if any.  This field is not
   // persistent though; its only used in the in-tab cookies dialog to show the
@@ -153,6 +159,9 @@
   bool secure_;
   bool httponly_;
   CookiePriority priority_;
+  // NOTE: When any new members are added above this comment, the
+  // implementation of Duplicate() must be updated to copy the new member
+  // accordingly.
 };
 
 typedef std::vector<CanonicalCookie> CookieList;