Address two review comments from 9531001.

runtime/vm/gc_marker.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/gc_marker.h"
 
 #include "vm/allocation.h"
 #include "vm/dart_api_state.h"
 #include "vm/isolate.h"
 #include "vm/pages.h"
@@ skipping 222 matching lines @@
 
 void GCMarker::IterateWeakRoots(Isolate* isolate, HandleVisitor* visitor) {
   isolate->VisitWeakPersistentHandles(visitor);
 }
 
 
 void GCMarker::IterateWeakReferences(Isolate* isolate,
                                      MarkingVisitor* visitor) {
   ApiState* state = isolate->api_state();
   ASSERT(state != NULL);
-  for (;;) {
+  while (true) {
     WeakReference* queue = state->delayed_weak_references();
     if (queue == NULL) {
-      break;
+      // The delay queue is empty therefore no clean-up is required.
+      return;
     }
     state->set_delayed_weak_references(NULL);
     while (queue != NULL) {
       WeakReference* reference = WeakReference::Pop(&queue);
       ASSERT(reference != NULL);
       bool is_unreachable = true;
       // Test each key object for reachability.  If a key object is
       // reachable, all value objects should be marked.
       for (intptr_t k = 0; k < reference->num_keys(); ++k) {
         if (!IsUnreachable(*reference->get_key(k))) {
@@ skipping 44 matching lines @@
   Prologue(isolate);
   MarkingVisitor mark(heap_, page_space, &marking_stack);
   IterateRoots(isolate, &mark);
   DrainMarkingStack(isolate, &mark);
   IterateWeakReferences(isolate, &mark);
   MarkingWeakVisitor mark_weak;
   IterateWeakRoots(isolate, &mark_weak);
 }
 
 }  // namespace dart