Avoid using a register for constant external array indices.

src/x64/lithium-codegen-x64.h

 // Copyright 2011 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 196 matching lines @@
   void AddToTranslation(Translation* translation,
                         LOperand* op,
                         bool is_tagged);
   void PopulateDeoptimizationData(Handle<Code> code);
   int DefineDeoptimizationLiteral(Handle<Object> literal);
 
   void PopulateDeoptimizationLiteralsWithInlinedFunctions();
 
   Register ToRegister(int index) const;
   XMMRegister ToDoubleRegister(int index) const;
+  Operand BuildExternalArrayOperand(LOperand* external_pointer,
+                                    LOperand* key,
+                                    ExternalArrayType array_type);
 
   // Specific math operations - used from DoUnaryMathOperation.
   void EmitIntegerMathAbs(LUnaryMathOperation* instr);
   void DoMathAbs(LUnaryMathOperation* instr);
   void DoMathFloor(LUnaryMathOperation* instr);
   void DoMathRound(LUnaryMathOperation* instr);
   void DoMathSqrt(LUnaryMathOperation* instr);
   void DoMathPowHalf(LUnaryMathOperation* instr);
   void DoMathLog(LUnaryMathOperation* instr);
   void DoMathCos(LUnaryMathOperation* instr);
@@ skipping 127 matching lines @@
  private:
   LCodeGen* codegen_;
   Label entry_;
   Label exit_;
   Label* external_exit_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_LITHIUM_CODEGEN_X64_H_