[vm, gc] Require a safepoint for heap iteration.

runtime/vm/isolate.cc

Index: runtime/vm/isolate.cc
diff --git a/runtime/vm/isolate.cc b/runtime/vm/isolate.cc
index 8589373d6fda2de551c70ceb77942a4a4ae4c2b7..6245f48222ac3f4d4cc5dc2500a78ac981568c92 100644
--- a/runtime/vm/isolate.cc
+++ b/runtime/vm/isolate.cc
@@ -1465,8 +1465,9 @@ static void ShutdownIsolate(uword parameter) {
       // This would otherwise happen in Dart::ShowdownIsolate.
       isolate->StopBackgroundCompiler();
       isolate->heap()->CollectAllGarbage();
+      HeapIterationScope iteration(thread);
       VerifyCanonicalVisitor check_canonical(thread);
-      isolate->heap()->IterateObjects(&check_canonical);
+      iteration.IterateObjects(&check_canonical);
     }
 #endif  // DEBUG
     const Error& error = Error::Handle(thread->sticky_error());
@@ -1738,18 +1739,6 @@ Monitor* Isolate::isolates_list_monitor_ = NULL;
 Isolate* Isolate::isolates_list_head_ = NULL;
 bool Isolate::creation_enabled_ = false;
 
-void Isolate::IterateObjectPointers(ObjectPointerVisitor* visitor,
-                                    bool validate_frames) {
-  HeapIterationScope heap_iteration_scope;
-  VisitObjectPointers(visitor, validate_frames);
-}
-
-void Isolate::IterateStackPointers(ObjectPointerVisitor* visitor,
-                                   bool validate_frames) {
-  HeapIterationScope heap_iteration_scope;
-  VisitStackPointers(visitor, validate_frames);
-}
-
 void Isolate::VisitObjectPointers(ObjectPointerVisitor* visitor,
                                   bool validate_frames) {
   ASSERT(visitor != NULL);