Use weak cells in dependent code.

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 4050 matching lines @@
     CHECK_EQ(new_count, (count + 1));
     site = Handle<AllocationSite>::cast(
         global_handles->Create(
             AllocationSite::cast(heap->allocation_sites_list())));
 
     CompileRun("%OptimizeFunctionOnNextCall(bar); bar();");
 
     DependentCode::GroupStartIndexes starts(site->dependent_code());
     CHECK_GE(starts.number_of_entries(), 1);
     int index = starts.at(DependentCode::kAllocationSiteTransitionChangedGroup);
-    CHECK(site->dependent_code()->is_code_at(index));
-    Code* function_bar = site->dependent_code()->code_at(index);
+    CHECK(site->dependent_code()->object_at(index)->IsWeakCell());
+    Code* function_bar = Code::cast(
+        WeakCell::cast(site->dependent_code()->object_at(index))->value());
     Handle<JSFunction> bar_handle =
         v8::Utils::OpenHandle(
             *v8::Handle<v8::Function>::Cast(
                 CcTest::global()->Get(v8_str("bar"))));
     CHECK_EQ(bar_handle->code(), function_bar);
   }
 
   // Now make sure that a gc should get rid of the function, even though we
   // still have the allocation site alive.
   for (int i = 0; i < 4; i++) {
     heap->CollectAllGarbage(Heap::kNoGCFlags);
   }
 
   // The site still exists because of our global handle, but the code is no
   // longer referred to by dependent_code().
   DependentCode::GroupStartIndexes starts(site->dependent_code());
   int index = starts.at(DependentCode::kAllocationSiteTransitionChangedGroup);
-  CHECK(!(site->dependent_code()->is_code_at(index)));
+  CHECK(site->dependent_code()->object_at(index)->IsWeakCell() &&
+        WeakCell::cast(site->dependent_code()->object_at(index))->cleared());
 }
 
 
 TEST(CellsInOptimizedCodeAreWeak) {
   if (i::FLAG_always_opt || !i::FLAG_crankshaft) return;
   i::FLAG_weak_embedded_objects_in_optimized_code = true;
   i::FLAG_allow_natives_syntax = true;
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   v8::internal::Heap* heap = CcTest::heap();
@@ skipping 883 matching lines @@
 #ifdef DEBUG
 TEST(PathTracer) {
   CcTest::InitializeVM();
   v8::HandleScope scope(CcTest::isolate());
 
   v8::Local<v8::Value> result = CompileRun("'abc'");
   Handle<Object> o = v8::Utils::OpenHandle(*result);
   CcTest::i_isolate()->heap()->TracePathToObject(*o);
 }
 #endif  // DEBUG