Switch to vectors instead of bare char* arrays.

src/fast-dtoa.h

 // Copyright 2010 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
@@ skipping 30 matching lines @@
 // There will be *length digits inside the buffer followed by a null terminator.
 // If the function returns true then
 //   v == (double) (buffer * 10^(point - length)).
 // The digits in the buffer are the shortest representation possible: no
 // 0.099999999999 instead of 0.1.
 // The last digit will be closest to the actual v. That is, even if several
 // digits might correctly yield 'v' when read again, the buffer will contain the
 // one closest to v.
 // The variable 'sign' will be '0' if the given number is positive, and '1'
 //   otherwise.
-bool FastDtoa(double d, char* buffer, int* sign, int* length, int* point);
+bool FastDtoa(double d,
+              Vector<char> buffer,
+              int* sign,
+              int* length,
+              int* point);
 
 } }  // namespace v8::internal
 
 #endif  // V8_FAST_DTOA_H_