Adding api to get last gc object statistics for chrome://tracing.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 71ee26e2cecc76f9784c8790947db2a4c226733f..8db8e49bd9bc701a414549e1e8e47be30dd4110d 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1017,6 +1017,13 @@ class Heap {
   // Print short heap statistics.
   void PrintShortHeapStatistics();
 
+  size_t object_count_last_gc(size_t type) {
+    return object_counts_last_time_[type];

[picksi, 2015/05/05 14:01:55]

Should we DCHECK the array bounds here for safety? e.g. type>=0 and
type<object_types?

[ssid, 2015/05/05 14:48:01]

Done.

+  }
+  size_t object_size_last_gc(size_t type) {
+    return object_sizes_last_time_[type];
+  }
+
   // Write barrier support for address[offset] = o.
   INLINE(void RecordWrite(Address address, int offset));
 
@@ -1445,6 +1452,7 @@ class Heap {
   void TraceObjectStats();
   void TraceObjectStat(const char* name, int count, int size, double time);
   void CheckpointObjectStats();
+  const char* GetObjectTypeName(size_t index);

[Primiano Tucci (use gerrit), 2015/05/05 14:17:53]

Should this be near the other ones you are adding?

[ssid, 2015/05/05 14:26:16]

the previous function does the same kind of operations. that is why this
function is added here. if the way in which the type index is handled changes,
then these functions change together.
Note: I am not sure if this function should be a part of Heap class. Maybe this
should be in objects.h . Waiting for owner's comment on that.

[ulan, 2015/05/06 12:46:02]

This place is correct. The "index" has meaning only in Heap because it is the
index in the object-stat table.

 
   // We don't use a LockGuard here since we want to lock the heap
   // only when FLAG_concurrent_recompilation is true.