Add an interface for an embedder to provide information about native

src/heap.h

Index: src/heap.h
diff --git a/src/heap.h b/src/heap.h
index 163eb04448328452f01b55a2edf0c5be98d6f816..98e661e52f577bccac90b037c6452a541467d367 100644
--- a/src/heap.h
+++ b/src/heap.h
@@ -1141,6 +1141,14 @@ class Heap : public AllStatic {
 
   static GCTracer* tracer() { return tracer_; }
 
+  static void CallGlobalGCPrologueCallback() {
+    if (global_gc_prologue_callback_ != NULL) global_gc_prologue_callback_();
+  }
+
+  static void CallGlobalGCEpilogueCallback() {
+    if (global_gc_epilogue_callback_ != NULL) global_gc_epilogue_callback_();
+  }
+
  private:
   static int reserved_semispace_size_;
   static int max_semispace_size_;