Add map-based read barrier to WeakCell

src/type-feedback-vector.cc

Index: src/type-feedback-vector.cc
diff --git a/src/type-feedback-vector.cc b/src/type-feedback-vector.cc
index 79afa2dad2dc31d60d735eaf9f746b1c917159c2..2994cd40d11d7b90989f11f8e135b1a126d8d717 100644
--- a/src/type-feedback-vector.cc
+++ b/src/type-feedback-vector.cc
@@ -393,7 +393,7 @@ int FeedbackNexus::ExtractMaps(int start_index, MapHandleList* maps) const {
     for (int i = start_index; i < array->length(); i += 2) {
       WeakCell* cell = WeakCell::cast(array->get(i));
       if (!cell->cleared()) {
-        Map* map = Map::cast(cell->value());
+        Map* map = Map::cast(cell->value(isolate->heap()));
         maps->Add(handle(map, isolate));
         found++;
       }
@@ -413,7 +413,10 @@ MaybeHandle<Code> FeedbackNexus::FindHandlerForMap(int start_index,
     for (int i = start_index; i < array->length(); i += 2) {
       WeakCell* cell = WeakCell::cast(array->get(i));
       if (!cell->cleared()) {
-        Map* array_map = Map::cast(cell->value());
+        // Don't need a read barrier because we immediately
+        // discard the value unless we already had it from
+        // somewhere else.
+        Map* array_map = Map::cast(cell->ValueNoReadBarrier());
         if (array_map == *map) {
           Code* code = Code::cast(array->get(i + 1));
           DCHECK(code->kind() == Code::HANDLER);