Include what you use for the preparser.

src/dtoa.h

Index: src/dtoa.h
diff --git a/src/dtoa.h b/src/dtoa.h
index 948a079191384ba14d3440786e5f45b1720949ea..5d9ed52a60aad38945b858b49fa06d037b0527ec 100644
--- a/src/dtoa.h
+++ b/src/dtoa.h
@@ -1,4 +1,4 @@
-// Copyright 2011 the V8 project authors. All rights reserved.
+// Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
@@ -31,6 +31,8 @@
 namespace v8 {
 namespace internal {
 
+template <typename T> class Vector;
+
 enum DtoaMode {
   // Return the shortest correct representation.
   // For example the output of 0.299999999999999988897 is (the less accurate but