Fix a potential crash bug in keyed calls for non-string keys.

src/x64/macro-assembler-x64.h

 // 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 643 matching lines @@
 
   // Abort execution if argument is not a number. Used in debug code.
   void AbortIfNotNumber(Register object);
 
   // Abort execution if argument is a smi. Used in debug code.
   void AbortIfSmi(Register object);
 
   // Abort execution if argument is not a smi. Used in debug code.
   void AbortIfNotSmi(Register object);
 
+  // Abort execution if argument is a string. Used in debug code.
+  void AbortIfNotString(Register object);
+
   // Abort execution if argument is not the root value with the given index.
   void AbortIfNotRootValue(Register src,
                            Heap::RootListIndex root_value_index,
                            const char* message);
 
   // ---------------------------------------------------------------------------
   // Exception handling
 
   // Push a new try handler and link into try handler chain.  The return
   // address must be pushed before calling this helper.
@@ skipping 1125 matching lines @@
       Jump(adaptor, RelocInfo::CODE_TARGET);
     }
     bind(&invoke);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_