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..73be627e206de38cd01c547a0063d899659f5ca7 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 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));
 
@@ -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);
 
   // We don't use a LockGuard here since we want to lock the heap
   // only when FLAG_concurrent_recompilation is true.