Include what you use for the preparser.

src/cached-powers.h

Index: src/cached-powers.h
diff --git a/src/cached-powers.h b/src/cached-powers.h
index 88df22260c3008c282e59d1ca52d18189fee3a4b..38892a72cf2ba205979feada2b772c4f1f009c07 100644
--- a/src/cached-powers.h
+++ b/src/cached-powers.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:
@@ -28,11 +28,11 @@
 #ifndef V8_CACHED_POWERS_H_
 #define V8_CACHED_POWERS_H_
 
-#include "diy-fp.h"
-
 namespace v8 {
 namespace internal {
 
+class DiyFp;
+
 class PowersOfTenCache {
  public:
   // Not all powers of ten are cached. The decimal exponent of two neighboring