Updates incremental marking pass to collect object statistics.

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index 471f7a6461cdd2ab133633c0dcbf4d3a02d42ab0..04606e34309abcbe2371027679b1092cd187c685 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -10,8 +10,9 @@
 #include "src/heap/gc-idle-time-handler.h"
 #include "src/heap/gc-tracer.h"
 #include "src/heap/mark-compact-inl.h"
-#include "src/heap/objects-visiting.h"
+#include "src/heap/object-stats.h"
 #include "src/heap/objects-visiting-inl.h"
+#include "src/heap/objects-visiting.h"
 #include "src/tracing/trace-event.h"
 #include "src/v8.h"
 
@@ -175,6 +176,9 @@ class IncrementalMarkingMarkingVisitor
     table_.Register(kVisitFixedArray, &VisitFixedArrayIncremental);
     table_.Register(kVisitNativeContext, &VisitNativeContextIncremental);
     table_.Register(kVisitJSRegExp, &VisitJSRegExp);
+    if (FLAG_trace_gc_object_stats) {
+      ObjectStatsVisitor::Initialize(&table_);
+    }

[mythria, 2016/05/03 16:04:34]

Hannes, I initialize the Visitor table only with IncrementalMarking visitor.
This means that objects visited during MarkCompact phase are not accounted for
in the object statistics. I think correct fix is to account for objects visited
during both these phases. Just wanted to check with you if my understanding is
correct before I implement it. 

If I understand correctly, if an object is marked during IncrementalMarking
phase it will not be marked again during MarkCompact phase. Otherwise, we may
count objects twice. 

[Hannes Payer (out of office), 2016/05/09 13:16:37]

That is correct. In case incremental marking is aborted you have to reset the
counters.

   }
 
   static const int kProgressBarScanningChunk = 32 * 1024;