Include what you use for the preparser.

src/strtod.h

Index: src/strtod.h
diff --git a/src/strtod.h b/src/strtod.h
index 1a5a96c8ebe1ef3eb519ba8526313b1fad2064a5..03e137524fc3233c96ede930b7709eb084b3b972 100644
--- a/src/strtod.h
+++ b/src/strtod.h
@@ -1,4 +1,4 @@
-// Copyright 2010 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;
+
 // The buffer must only contain digits in the range [0-9]. It must not
 // contain a dot or a sign. It must not start with '0', and must not be empty.
 double Strtod(Vector<const char> buffer, int exponent);