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 dfbcc701e6939f5a7215d19c9118f09440fe9121..6a3e769749b4db5a169924fde56d62bd8fab7641 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1022,6 +1022,13 @@ class Heap {
   // Print short heap statistics.
   void PrintShortHeapStatistics();
 
+  size_t object_count_last_gc(size_t index) {
+    return index < OBJECT_STATS_COUNT ? object_counts_last_time_[index] : 0;
+  }
+  size_t object_size_last_gc(size_t index) {
+    return index < OBJECT_STATS_COUNT ? object_sizes_last_time_[index] : 0;
+  }
+
   // Write barrier support for address[offset] = o.
   INLINE(void RecordWrite(Address address, int offset));
 
@@ -1452,6 +1459,8 @@ class Heap {
   void TraceObjectStats();
   void TraceObjectStat(const char* name, int count, int size, double time);
   void CheckpointObjectStats();
+  bool GetObjectTypeName(size_t index, const char** object_type,
+                         const char** object_sub_type);
 
   void RegisterStrongRoots(Object** start, Object** end);
   void UnregisterStrongRoots(Object** start);