Restructure/fix thread pointer visiting; added some asserts.

runtime/vm/thread.cc

Index: runtime/vm/thread.cc
diff --git a/runtime/vm/thread.cc b/runtime/vm/thread.cc
index 90dfaef6d0aa8a93e3d18a05537d1581e33ded52..ed0808823bd2df309fb374d500ec046a095670f3 100644
--- a/runtime/vm/thread.cc
+++ b/runtime/vm/thread.cc
@@ -359,9 +359,14 @@ void Thread::ClearReusableHandles() {
 }
 
 
-void Thread::VisitObjectPointers(ObjectPointerVisitor* visitor) {
+void Thread::VisitObjectPointers(ObjectPointerVisitor* visitor,
+                                 bool validate_frames) {
   ASSERT(visitor != NULL);
 
+  if (zone_ != NULL) {
+    zone_->VisitObjectPointers(visitor);
+  }
+
   // Visit objects in thread specific handles area.
   reusable_handles_.VisitObjectPointers(visitor);
 
@@ -376,6 +381,15 @@ void Thread::VisitObjectPointers(ObjectPointerVisitor* visitor) {
     scope->local_handles()->VisitObjectPointers(visitor);
     scope = scope->previous();
   }
+
+  // Iterate over all the stack frames and visit objects on the stack.
+  StackFrameIterator frames_iterator(top_exit_frame_info(),
+                                     validate_frames);
+  StackFrame* frame = frames_iterator.NextFrame();
+  while (frame != NULL) {
+    frame->VisitObjectPointers(visitor);
+    frame = frames_iterator.NextFrame();
+  }
 }