Fix GenerateNegativeLookup to work with non-symbols as a dictionary key.

src/x64/stub-cache-x64.cc

 // Copyright 2010 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 146 matching lines @@
     __ movq(entity_name, Operand(properties, index, times_pointer_size,
                                  kElementsStartOffset - kHeapObjectTag));
     __ Cmp(entity_name, Factory::undefined_value());
     // __ jmp(miss_label);
     if (i != kProbes - 1) {
       __ j(equal, &done);
 
       // Stop if found the property.
       __ Cmp(entity_name, Handle<String>(name));
       __ j(equal, miss_label);
+
+      // Check if the entry name is not a symbol.
+      __ movq(entity_name, FieldOperand(entity_name, HeapObject::kMapOffset));
+      __ testb(FieldOperand(entity_name, Map::kInstanceTypeOffset),
+               Immediate(kIsSymbolMask));
+      __ j(zero, miss_label);
     } else {
       // Give up probing if still not found the undefined value.
       __ j(not_equal, miss_label);
     }
   }
 
   __ bind(&done);
   __ DecrementCounter(&Counters::negative_lookups_miss, 1);
 }
 
@@ skipping 2368 matching lines @@
   // Return the generated code.
   return GetCode();
 }
 
 
 #undef __
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64