[heap] Simplify clearing of normalized map caches.

src/heap/objects-visiting-inl.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_VISITING_INL_H_
 #define V8_OBJECTS_VISITING_INL_H_
 
 #include "src/heap/array-buffer-tracker.h"
 #include "src/heap/mark-compact.h"
 #include "src/heap/objects-visiting.h"
@@ skipping 277 matching lines @@
 void StaticMarkingVisitor<StaticVisitor>::VisitBytecodeArray(
     Map* map, HeapObject* object) {
   FixedBodyVisitor<StaticVisitor, BytecodeArray::MarkingBodyDescriptor,
                    void>::Visit(map, object);
   BytecodeArray::cast(object)->MakeOlder();
 }
 
 template <typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitNativeContext(
     Map* map, HeapObject* object) {
+  // GC can happen when the context is not fully initialized,
+  // so the cache can be undefined.
+  Object* cache =
+      Context::cast(object)->get(Context::NORMALIZED_MAP_CACHE_INDEX);
+  if (cache->IsNormalizedMapCache()) {
+    NormalizedMapCache::cast(cache)->Clear();
+  }
   FixedBodyVisitor<StaticVisitor, Context::MarkCompactBodyDescriptor,
                    void>::Visit(map, object);
 }
 
 
 template <typename StaticVisitor>
 void StaticMarkingVisitor<StaticVisitor>::VisitMap(Map* map,
                                                    HeapObject* object) {
   Heap* heap = map->GetHeap();
   Map* map_object = Map::cast(object);
@@ skipping 331 matching lines @@
   typedef FlexibleBodyVisitor<StaticVisitor, JSFunction::BodyDescriptorWeakCode,
                               void> JSFunctionWeakCodeBodyVisitor;
   JSFunctionWeakCodeBodyVisitor::Visit(map, object);
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_OBJECTS_VISITING_INL_H_