Update V8 to 3.12.

deps/all.deps/DEPS

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 vars = {
   "gyp_rev": "@1451",
   "co19_rev": "@290",
   "co19_repo": "http://co19.googlecode.com/svn/trunk/co19/",
   "chromium_url": "http://src.chromium.org/svn",
+  "v8_version": "3.12",
 }
 
 deps = {
   "dart":
     "/branches/bleeding_edge/dart",
 
   # Stuff needed for GYP to run.
   "dart/third_party/gyp":
     "http://gyp.googlecode.com/svn/trunk" + Var("gyp_rev"),
 
   "dart/third_party/v8":
-    "http://v8.googlecode.com/svn/branches/3.10",
+    "http://v8.googlecode.com/svn/branches/" + Var("v8_version"),
 
   "dart/tests/co19/src":
     Var("co19_repo") + "tests/co19/src" + Var("co19_rev"),
 }
 
 deps_os = {
   "win": {
     "dart/third_party/cygwin":
       Var("chromium_url") + "/trunk/deps/third_party/cygwin@66844",
   },
@@ skipping 12 matching lines @@
   },
   {
     "pattern": ".",
     "action": ["python", "dart/tools/generate_projects.py", "compiler"],
   },
   {
     "pattern": ".",
     "action": ["python", "dart/tools/gyp_dart.py"],
   }
 ]