Fix compilation failure on Win.

src/heap.h

 // Copyright 2006-2008 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 1264 matching lines @@
 
   static void UpdateSurvivalRateTrend(int start_new_space_size);
 
   enum SurvivalRateTrend { INCREASING, STABLE, DECREASING, FLUCTUATING };
 
   static const int kYoungSurvivalRateThreshold = 90;
   static const int kYoungSurvivalRateAllowedDeviation = 15;
 
   static int young_survivors_after_last_gc_;
   static int high_survival_rate_period_length_;
-  static int survival_rate_;
+  static double survival_rate_;
   static SurvivalRateTrend previous_survival_rate_trend_;
   static SurvivalRateTrend survival_rate_trend_;
   static bool bumped_old_gen_limits_;
 
   static void set_survival_rate_trend(SurvivalRateTrend survival_rate_trend) {
     ASSERT(survival_rate_trend != FLUCTUATING);
     previous_survival_rate_trend_ = survival_rate_trend_;
     survival_rate_trend_ = survival_rate_trend;
   }
 
@@ skipping 689 matching lines @@
 
   // To speed up scavenge collections new space string are kept
   // separate from old space strings.
   static List<Object*> new_space_strings_;
   static List<Object*> old_space_strings_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_