Update V8 to version 2.2.18.

This version contains API additions for heap profiling and fetching information on external arrays.  It fixes a bug, implementing Object.defineProperty for array elements.  Adds a couple of minor performance improvements.

BUG=None
TEST=None

Review URL: http://codereview.chromium.org/2817006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@49932 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -52,7 +52,7 @@ deps = {
     "http://gyp.googlecode.com/svn/trunk@826",
 
   "src/v8":
-    "http://v8.googlecode.com/svn/trunk@4851",
+    "http://v8.googlecode.com/svn/trunk@4875",
 
   "src/native_client":
     "http://nativeclient.googlecode.com/svn/trunk/src/native_client@" +