Fix responsiveness of high promotion mode heuristics.

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 6dc9d61117d93ff34041c093db077111a2a47ef6..d47d2a58bcce88184db0f89dd6946980ad3fb375 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1381,6 +1381,7 @@ class Heap {
   void CheckNewSpaceExpansionCriteria();
 
   inline void IncrementYoungSurvivorsCounter(int survived) {
+    ASSERT(survived >= 0);
     young_survivors_after_last_gc_ = survived;
     survived_since_last_expansion_ += survived;
   }
@@ -1799,11 +1800,13 @@ class Heap {
 
   enum SurvivalRateTrend { INCREASING, STABLE, DECREASING, FLUCTUATING };
 
-  static const int kYoungSurvivalRateThreshold = 90;
+  static const int kYoungSurvivalRateHighThreshold = 90;
+  static const int kYoungSurvivalRateLowThreshold = 10;
   static const int kYoungSurvivalRateAllowedDeviation = 15;
 
   int young_survivors_after_last_gc_;
   int high_survival_rate_period_length_;
+  int low_survival_rate_period_length_;
   double survival_rate_;
   SurvivalRateTrend previous_survival_rate_trend_;
   SurvivalRateTrend survival_rate_trend_;
@@ -1836,18 +1839,28 @@ class Heap {
     }
   }
 
-  bool IsIncreasingSurvivalTrend() {
-    return survival_rate_trend() == INCREASING;
+  bool IsStableOrDecreasingSurvivalTrend() {
+    switch (survival_rate_trend()) {
+      case STABLE:
+      case DECREASING:
+        return true;
+      default:
+        return false;
+    }
   }
 
-  bool IsDecreasingSurvivalTrend() {
-    return survival_rate_trend() == DECREASING;
+  bool IsIncreasingSurvivalTrend() {
+    return survival_rate_trend() == INCREASING;
   }
 
   bool IsHighSurvivalRate() {
     return high_survival_rate_period_length_ > 0;
   }
 
+  bool IsLowSurvivalRate() {
+    return low_survival_rate_period_length_ > 0;
+  }
+
   void SelectScavengingVisitorsTable();
 
   void StartIdleRound() {