v8:3539 - hold constructor feedback in weak cells

test/cctest/test-feedback-vector.cc

Index: test/cctest/test-feedback-vector.cc
diff --git a/test/cctest/test-feedback-vector.cc b/test/cctest/test-feedback-vector.cc
index f53dfde10e4e871f3f4416bd5bd57d40521b0b2e..464a0a724a12e6a50bcc822d8f8bf7e56aff854a 100644
--- a/test/cctest/test-feedback-vector.cc
+++ b/test/cctest/test-feedback-vector.cc
@@ -140,13 +140,19 @@ TEST(VectorSlotClearing) {
 
   // Fill with information
   vector->Set(FeedbackVectorSlot(0), Smi::FromInt(1));
-  vector->Set(FeedbackVectorSlot(1), *factory->fixed_array_map());
+  Handle<WeakCell> cell = factory->NewWeakCell(factory->fixed_array_map());
+  vector->Set(FeedbackVectorSlot(1), *cell);
   Handle<AllocationSite> site = factory->NewAllocationSite();
   vector->Set(FeedbackVectorSlot(2), *site);
 
+  // GC time clearing leaves slots alone.
+  vector->ClearSlotsAtGCTime(NULL);
+  Object* obj = vector->Get(FeedbackVectorSlot(1));
+  CHECK(obj->IsWeakCell() && !WeakCell::cast(obj)->cleared());
+
   vector->ClearSlots(NULL);
 
-  // The feedback vector slots are cleared. AllocationSites are granted
+  // The feedback vector slots are cleared. AllocationSites are still granted
   // an exemption from clearing, as are smis.
   CHECK_EQ(Smi::FromInt(1), vector->Get(FeedbackVectorSlot(0)));
   CHECK_EQ(*TypeFeedbackVector::UninitializedSentinel(isolate),