Restore frame validation (fixes to CL faaf60801f72).

runtime/vm/thread_registry.h

Index: runtime/vm/thread_registry.h
diff --git a/runtime/vm/thread_registry.h b/runtime/vm/thread_registry.h
index b7d3e1a8a0877f2e1217c8c0925b77dc46be71be..efe81bdcfa69ca8540760424d8a289bca8943275 100644
--- a/runtime/vm/thread_registry.h
+++ b/runtime/vm/thread_registry.h
@@ -115,7 +115,8 @@ class ThreadRegistry {
     }
   }
 
-  void VisitObjectPointers(ObjectPointerVisitor* visitor) {
+  void VisitObjectPointers(ObjectPointerVisitor* visitor,
+                           bool validate_frames) {
     MonitorLocker ml(monitor_);
     for (int i = 0; i < entries_.length(); ++i) {
       const Entry& entry = entries_[i];
@@ -125,9 +126,8 @@ class ThreadRegistry {
         state.zone->VisitObjectPointers(visitor);
       }
       // Iterate over all the stack frames and visit objects on the stack.
-      uword efi = state.top_exit_frame_info;
-      if (efi == 0) continue;
-      StackFrameIterator frames_iterator(efi, false);
+      StackFrameIterator frames_iterator(state.top_exit_frame_info,
+                                         validate_frames);
       StackFrame* frame = frames_iterator.NextFrame();
       while (frame != NULL) {
         frame->VisitObjectPointers(visitor);