Add option to compute average scavenge speed w.r.t survived objects.

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 9a7b28d4fb5624481b1b283c9d5332715d18f323..468fc9c0be7c4c298e2eb6a03580ff6be66f6505 100644
--- a/src/heap/gc-tracer.h
+++ b/src/heap/gc-tracer.h
@@ -85,6 +85,9 @@ class RingBuffer {
 };
 
 
+enum ScavengeSpeedMode { kForAllObjects, kForSurvivedObjects };
+
+
 // GCTracer collects and prints ONE line after each garbage collector
 // invocation IFF --trace_gc is used.
 // TODO(ernstm): Unit tests.
@@ -227,6 +230,8 @@ class GCTracer {
 
     // Size of new space objects in constructor.
     intptr_t new_space_object_size;
+    // Size of survived new space objects in desctructor.
+    intptr_t survived_new_space_object_size;
 
     // Number of incremental marking steps since creation of tracer.
     // (value at start of event)
@@ -371,7 +376,8 @@ class GCTracer {
 
   // Compute the average scavenge speed in bytes/millisecond.
   // Returns 0 if no events have been recorded.
-  intptr_t ScavengeSpeedInBytesPerMillisecond() const;
+  intptr_t ScavengeSpeedInBytesPerMillisecond(
+      ScavengeSpeedMode mode = kForAllObjects) const;
 
   // Compute the average mark-sweep speed in bytes/millisecond.
   // Returns 0 if no events have been recorded.