Use weak cell to embed map in CompareNil IC.

src/hydrogen.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_HYDROGEN_H_
 #define V8_HYDROGEN_H_
 
 #include "src/v8.h"
 
 #include "src/accessors.h"
@@ skipping 1846 matching lines @@
                                       HValue* allocation_site,
                                       AllocationSiteMode mode);
 
   HValue* BuildCloneShallowArrayNonEmpty(HValue* boilerplate,
                                          HValue* allocation_site,
                                          AllocationSiteMode mode,
                                          ElementsKind kind);
 
   HValue* BuildElementIndexHash(HValue* index);
 
-  void BuildCompareNil(
-      HValue* value,
-      Type* type,
-      HIfContinuation* continuation);
+  enum MapEmbedding { kEmbedMapsDirectly, kEmbedMapsViaWeakCells };
+
+  void BuildCompareNil(HValue* value, Type* type, HIfContinuation* continuation,
+                       MapEmbedding map_embedding = kEmbedMapsDirectly);
 
   void BuildCreateAllocationMemento(HValue* previous_object,
                                     HValue* previous_object_size,
                                     HValue* payload);
 
   HInstruction* BuildConstantMapCheck(Handle<JSObject> constant);
   HInstruction* BuildCheckPrototypeMaps(Handle<JSObject> prototype,
                                         Handle<JSObject> holder);
 
   HInstruction* BuildGetNativeContext(HValue* closure);
@@ skipping 1061 matching lines @@
   }
 
  private:
   HGraphBuilder* builder_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_H_