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

runtime/vm/profiler.cc

Index: runtime/vm/profiler.cc
diff --git a/runtime/vm/profiler.cc b/runtime/vm/profiler.cc
index a99b48ee84b38090e31fdc1e74dc7b6e2eef88a3..7acf9f1e02c37de74e3b68d53997c85ab0d54360 100644
--- a/runtime/vm/profiler.cc
+++ b/runtime/vm/profiler.cc
@@ -1427,9 +1427,12 @@ void CodeLookupTable::Build(Thread* thread) {
   code_objects_.Clear();
 
   // Add all found Code objects.
-  CodeLookupTableBuilder cltb(this);
-  vm_isolate->heap()->IterateOldObjects(&cltb);
-  isolate->heap()->IterateOldObjects(&cltb);
+  {
+    HeapIterationScope iteration;
+    CodeLookupTableBuilder cltb(this);
+    iteration.IterateVMIsolateObjects(&cltb);
+    iteration.IterateOldObjects(&cltb);
+  }
 
   // Sort by entry.
   code_objects_.Sort(CodeDescriptor::Compare);