Include what you use for the preparser.

src/fixed-dtoa.h

Index: src/fixed-dtoa.h
diff --git a/src/fixed-dtoa.h b/src/fixed-dtoa.h
index 93f826fe841452ca3db738abb27ee477992fb15a..bf1aab99fb0f3f4d8674356f9c7a0b9d513a7097 100644
--- a/src/fixed-dtoa.h
+++ b/src/fixed-dtoa.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;
+
 // Produces digits necessary to print a given number with
 // 'fractional_count' digits after the decimal point.
 // The buffer must be big enough to hold the result plus one terminating null