Include what you use for the preparser.

src/cached-powers.h

-// 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:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
 //       with the distribution.
 //     * Neither the name of Google Inc. nor the names of its
 //       contributors may be used to endorse or promote products derived
 //       from this software without specific prior written permission.
 //
 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #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
   // cached numbers will differ by kDecimalExponentDistance.
   static const int kDecimalExponentDistance;
 
   static const int kMinDecimalExponent;
   static const int kMaxDecimalExponent;
 
   // Returns a cached power-of-ten with a binary exponent in the range
   // [min_exponent; max_exponent] (boundaries included).
   static void GetCachedPowerForBinaryExponentRange(int min_exponent,
                                                    int max_exponent,
                                                    DiyFp* power,
                                                    int* decimal_exponent);
 
   // Returns a cached power of ten x ~= 10^k such that
   //   k <= decimal_exponent < k + kCachedPowersDecimalDistance.
   // The given decimal_exponent must satisfy
   //   kMinDecimalExponent <= requested_exponent, and
   //   requested_exponent < kMaxDecimalExponent + kDecimalExponentDistance.
   static void GetCachedPowerForDecimalExponent(int requested_exponent,
                                                DiyFp* power,
                                                int* found_exponent);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CACHED_POWERS_H_