Make sure double to int conversion is correct.

src/conversions.h

 // Copyright 2011 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 41 matching lines @@
 }
 
 
 inline double SignedZero(bool negative) {
   return negative ? -0.0 : 0.0;
 }
 
 
 // The fast double-to-(unsigned-)int conversion routine does not guarantee
 // rounding towards zero.
+// For NaN and values outside the int range, return INT_MIN or INT_MAX.
+inline int FastD2IChecked(double x) {
+  if (!(x >= INT_MIN)) return INT_MIN;  // Negation to catch NaNs.
+  if (x > INT_MAX) return INT_MAX;
+  return static_cast<int>(x);
+}
+
+
+// The fast double-to-(unsigned-)int conversion routine does not guarantee
+// rounding towards zero.
 // The result is unspecified if x is infinite or NaN, or if the rounded
 // integer value is outside the range of type int.
 inline int FastD2I(double x) {
-  // The static_cast convertion from double to int used to be slow, but
-  // as new benchmarks show, now it is much faster than lrint().
   return static_cast<int>(x);
 }
 
+
 inline unsigned int FastD2UI(double x);
 
 
 inline double FastI2D(int x) {
   // There is no rounding involved in converting an integer to a
   // double, so this code should compile to a few instructions without
   // any FPU pipeline stalls.
   return static_cast<double>(x);
 }
 
@@ skipping 59 matching lines @@
 // Additional number to string conversions for the number type.
 // The caller is responsible for calling free on the returned pointer.
 char* DoubleToFixedCString(double value, int f);
 char* DoubleToExponentialCString(double value, int f);
 char* DoubleToPrecisionCString(double value, int f);
 char* DoubleToRadixCString(double value, int radix);
 
 } }  // namespace v8::internal
 
 #endif  // V8_CONVERSIONS_H_