Revert of [heap] Do not invoke GC to make heap iterable.

src/runtime/runtime-debug.cc

Index: src/runtime/runtime-debug.cc
diff --git a/src/runtime/runtime-debug.cc b/src/runtime/runtime-debug.cc
index 15e72e7598cc884e35585e413dd71d69ed24e7fa..e3f3beb6976da53443707168c427ff0247e525ed 100644
--- a/src/runtime/runtime-debug.cc
+++ b/src/runtime/runtime-debug.cc
@@ -1231,7 +1231,7 @@
   List<Handle<JSObject> > instances;
   Heap* heap = isolate->heap();
   {
-    HeapIterator iterator(heap, HeapObjectsFiltering::kFilterUnreachable);
+    HeapIterator iterator(heap, HeapIterator::kFilterUnreachable);
     // Get the constructor function for context extension and arguments array.
     Object* arguments_fun = isolate->sloppy_arguments_map()->GetConstructor();
     HeapObject* heap_obj;
@@ -1286,7 +1286,7 @@
   List<Handle<JSObject> > instances;
   Heap* heap = isolate->heap();
   {
-    HeapIterator iterator(heap, HeapObjectsFiltering::kFilterUnreachable);
+    HeapIterator iterator(heap, HeapIterator::kFilterUnreachable);
     HeapObject* heap_obj;
     while ((heap_obj = iterator.next())) {
       if (!heap_obj->IsJSObject()) continue;