Add regression test for r10451.

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 7015a1ee625212eedb31ac7aa6965e49133686fb..1595fc5d958e535d308e83cc36377c59cfb34ad0 100644
--- a/test/cctest/test-heap.cc
+++ b/test/cctest/test-heap.cc
@@ -1606,4 +1606,22 @@ TEST(PrototypeTransitionClearing) {
     CHECK(trans->get(j + Map::kProtoTransitionMapOffset)->IsMap());
     CHECK(trans->get(j + Map::kProtoTransitionPrototypeOffset)->IsJSObject());
   }
+
+  // Make sure next prototype is placed on an old-space evacuation candidate.
+  PagedSpace* space = HEAP->old_pointer_space();
+  while (space->FirstPage() == space->LastPage()) {
+    FACTORY->NewJSArray(1, TENURED);

[Vyacheslav Egorov (Chromium), 2012/01/20 12:17:39]

This loop looks a bit spooky because the fact that NewJSArray returns a handle
is kinda hidden so one would expect that these arrays will die and this will
cause infinite loop (but they don't because they actually are referenced from
the local handles).

Please add a comment about this. Also it might sense to use bigger arrays to
make this test complete faster.

[Michael Starzinger, 2012/01/20 12:41:53]

Done. Now unnecessary due to second change.

+  }
+
+  // Add a prototype on an evacuation candidate and verify that transition
+  // clearing correctly records slots in prototype transition array.
+  i::FLAG_always_compact = true;
+  Handle<Map> map(baseObject->map());
+  Handle<JSObject> prototype = FACTORY->NewJSArray(0, TENURED);
+  CHECK(!space->LastPage()->Contains(map->prototype_transitions()->address()));

[Vyacheslav Egorov (Chromium), 2012/01/20 12:17:39]

this check look suspicious. by accident there might be a hole on the first page
large enough for this object. You might consider changing the first loop into 


Handle<JSObject> prototype;

do {
prototype = FACTORY->NewJSArray(N, TENURED);
} while (prototype is not on the second page);

[Michael Starzinger, 2012/01/20 12:41:53]

Done. Yes, that is much simpler and I can arbitrarily increase the size of the
prototype without worrying about holes in the free-list. That makes the test
complete much faster. Nice idea!

+  CHECK(space->LastPage()->Contains(prototype->address()));
+  baseObject->SetPrototype(*prototype, false)->ToObjectChecked();
+  CHECK(map->GetPrototypeTransition(*prototype)->IsMap());
+  HEAP->CollectAllGarbage(Heap::kNoGCFlags);
+  CHECK(map->GetPrototypeTransition(*prototype)->IsMap());
 }