Apply V8 r5951 to fix Mac build

From f3973972b727df480697443871d780596aba0201 Mon Sep 17 00:00:00 2001
From: erik.corry@gmail.com <erik.corry@gmail.com@ce2b1a6d-e550-0410-aec6-3dcde31c8c00>
Date: Wed, 8 Dec 2010 16:23:25 +0000
Subject: [PATCH] Speed up quoting of JSON strings by allocating a string that is big enough
 and then trimming it when the length is known.  This way we only have to
 traverse the input once.
 Review URL: http://codereview.chromium.org/5556012