Decrease OldSurvivalRateLowThreshold to fit heap growing strategy.

BUG=
R=mvstanton@chromium.org

Review URL: https://codereview.chromium.org/282223005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21327 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/heap.h

@@ -2025,7 +2025,7 @@ class Heap {
   static const int kYoungSurvivalRateLowThreshold = 10;
   static const int kYoungSurvivalRateAllowedDeviation = 15;
 
-  static const int kOldSurvivalRateLowThreshold = 20;
+  static const int kOldSurvivalRateLowThreshold = 10;
 
   int young_survivors_after_last_gc_;
   int high_survival_rate_period_length_;