Include what you use for the preparser.

src/fast-dtoa.h

-// 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:
 //
 //     * 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.
@@ skipping 12 matching lines @@
 // 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_FAST_DTOA_H_
 #define V8_FAST_DTOA_H_
 
 namespace v8 {
 namespace internal {
 
+template <typename T> class Vector;
+
 enum FastDtoaMode {
   // Computes the shortest representation of the given input. The returned
   // result will be the most accurate number of this length. Longer
   // representations might be more accurate.
   FAST_DTOA_SHORTEST,
   // Computes a representation where the precision (number of digits) is
   // given as input. The precision is independent of the decimal point.
   FAST_DTOA_PRECISION
 };
 
@@ skipping 30 matching lines @@
 bool FastDtoa(double d,
               FastDtoaMode mode,
               int requested_digits,
               Vector<char> buffer,
               int* length,
               int* decimal_point);
 
 } }  // namespace v8::internal
 
 #endif  // V8_FAST_DTOA_H_