Make Failure inherit from MaybeObject instead of Object.

src/property.h

 // Copyright 2006-2008 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 27 matching lines @@
 // property index (in the actual instance-descriptor array) and
 // optionally a piece of data.
 //
 
 class Descriptor BASE_EMBEDDED {
  public:
   static int IndexFromValue(Object* value) {
     return Smi::cast(value)->value();
   }
 
-  Object* KeyToSymbol() {
+  MUST_USE_RESULT MaybeObject* KeyToSymbol() {
     if (!StringShape(key_).IsSymbol()) {
-      Object* result = Heap::LookupSymbol(key_);
-      if (result->IsFailure()) return result;
+      Object* result;
+      { MaybeObject* maybe_result = Heap::LookupSymbol(key_);
+        if (!maybe_result->ToObject(&result)) return maybe_result;
+      }
       key_ = String::cast(result);
     }
     return key_;
   }
 
   String* GetKey() { return key_; }
   Object* GetValue() { return value_; }
   PropertyDetails GetDetails() { return details_; }
 
 #ifdef DEBUG
@@ skipping 244 matching lines @@
   JSObject* holder_;
   int number_;
   bool cacheable_;
   PropertyDetails details_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROPERTY_H_