Shrink initial old generation size based on new space survival rate.

src/heap/gc-tracer.h

Index: src/heap/gc-tracer.h
diff --git a/src/heap/gc-tracer.h b/src/heap/gc-tracer.h
index 6932eadfd8d4ea4298bed4ff9d06c0c488b5759a..a2e4bc293eefc4366d500fcc81ea945c828a33b0 100644
--- a/src/heap/gc-tracer.h
+++ b/src/heap/gc-tracer.h
@@ -159,6 +159,17 @@ class GCTracer {
   };
 
 
+  class SurvivalEvent {
+   public:
+    // Default constructor leaves the event uninitialized.
+    SurvivalEvent() {}
+
+    explicit SurvivalEvent(double survival_rate);
+
+    double survival_rate_;
+  };
+
+
   class Event {
    public:
     enum Type {
@@ -267,6 +278,8 @@ class GCTracer {
   typedef RingBuffer<ContextDisposalEvent, kRingBufferMaxSize>
       ContextDisposalEventBuffer;
 
+  typedef RingBuffer<SurvivalEvent, kRingBufferMaxSize> SurvivalEventBuffer;
+
   explicit GCTracer(Heap* heap);
 
   // Start collecting data.
@@ -281,6 +294,8 @@ class GCTracer {
 
   void AddContextDisposalTime(double time);
 
+  void AddSurvivalRate(double survival_rate);
+
   // Log an incremental marking step.
   void AddIncrementalMarkingStep(double duration, intptr_t bytes);
 
@@ -367,6 +382,14 @@ class GCTracer {
   // Returns 0 if no events have been recorded.
   double ContextDisposalRateInMilliseconds() const;
 
+  // Computes the average survival rate based on the last recorded survival
+  // events.
+  // Returns 0 if no events have been recorded.
+  double AverageSurvivalRate() const;
+
+  // Returns true if at least one survival event was recorded.
+  bool SurvivalEventsRecorded() const;
+
  private:
   // Print one detailed trace line in name=value format.
   // TODO(ernstm): Move to Heap.
@@ -417,8 +440,12 @@ class GCTracer {
   // RingBuffer for allocation events.
   AllocationEventBuffer allocation_events_;
 
+  // RingBuffer for context disposal events.
   ContextDisposalEventBuffer context_disposal_events_;
 
+  // RingBuffer for survival events.
+  SurvivalEventBuffer survival_events_;
+
   // Cumulative number of incremental marking steps since creation of tracer.
   int cumulative_incremental_marking_steps_;