Update V8 to r3431 as required by WebKit r51976.

Change-Id: I567392c3f8c0a0d5201a4249611ac4ccf468cd5b
diff --git a/tools/utils.py b/tools/utils.py
index 78d1e0d..196bb05 100644
--- a/tools/utils.py
+++ b/tools/utils.py
@@ -55,6 +55,8 @@
     return 'win32'
   elif id == 'FreeBSD':
     return 'freebsd'
+  elif id == 'OpenBSD':
+    return 'openbsd'
   else:
     return None