Fix Iteration on gc stress builder.

test/cctest/test-heap.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 859 matching lines @@
     CHECK_EQ(length, ascii_str->length());
     DeleteArray(non_ascii);
     DeleteArray(ascii);
   }
 }
 
 
 static int ObjectsFoundInHeap(Heap* heap, Handle<Object> objs[], int size) {
   // Count the number of objects found in the heap.
   int found_count = 0;
+  heap->EnsureHeapIsIterable();
   HeapIterator iterator(heap);
   for (HeapObject* obj = iterator.next(); obj != NULL; obj = iterator.next()) {
     for (int i = 0; i < size; i++) {
       if (*objs[i] == obj) {
         found_count++;
       }
     }
   }
   return found_count;
 }
@@ skipping 2282 matching lines @@
              "    var a = new Array(n);"
              "    for (var i = 0; i < n; i += 100) a[i] = i;"
              "};"
              "f(10 * 1024 * 1024);");
   IncrementalMarking* marking = HEAP->incremental_marking();
   if (marking->IsStopped()) marking->Start();
   // This big step should be sufficient to mark the whole array.
   marking->Step(100 * MB, IncrementalMarking::NO_GC_VIA_STACK_GUARD);
   ASSERT(marking->IsComplete());
 }