Fix Iteration on gc stress builder.

test/cctest/test-heap.cc

Index: test/cctest/test-heap.cc
diff --git a/test/cctest/test-heap.cc b/test/cctest/test-heap.cc
index d60deedf9f65bd80893c616f6b2200c342679ea8..3dda81360feaabece6f20e977d63caab241ae58b 100644
--- a/test/cctest/test-heap.cc
+++ b/test/cctest/test-heap.cc
@@ -877,6 +877,7 @@ TEST(StringAllocation) {
 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++) {