Use weak cell to embed map in CompareNil IC.

src/hydrogen-instructions.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_INSTRUCTIONS_H_
 #define V8_HYDROGEN_INSTRUCTIONS_H_
 
 #include <iosfwd>
 
 #include "src/v8.h"
@@ skipping 6233 matching lines @@
   }
 
   static HObjectAccess ForPropertyCellValue() {
     return HObjectAccess(kInobject, PropertyCell::kValueOffset);
   }
 
   static HObjectAccess ForCellValue() {
     return HObjectAccess(kInobject, Cell::kValueOffset);
   }
 
+  static HObjectAccess ForWeakCellValue() {
+    return HObjectAccess(kInobject, WeakCell::kValueOffset);
+  }
+
   static HObjectAccess ForAllocationMementoSite() {
     return HObjectAccess(kInobject, AllocationMemento::kAllocationSiteOffset);
   }
 
   static HObjectAccess ForCounter() {
     return HObjectAccess(kExternalMemory, 0, Representation::Integer32(),
                          Handle<String>::null(), false, false);
   }
 
   static HObjectAccess ForExternalUInteger8() {
@@ skipping 1756 matching lines @@
 };
 
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_