Improve implementation of HSeqStringSetChar.

src/x64/lithium-codegen-x64.h

 // Copyright 2012 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 224 matching lines @@
 
   Register ToRegister(int index) const;
   XMMRegister ToDoubleRegister(int index) const;
   Operand BuildFastArrayOperand(
       LOperand* elements_pointer,
       LOperand* key,
       ElementsKind elements_kind,
       uint32_t offset,
       uint32_t additional_index = 0);
 
+  Operand BuildSeqStringOperand(Register string,
+                                LOperand* index,
+                                String::Encoding encoding);
+
   void EmitIntegerMathAbs(LMathAbs* instr);
   void EmitSmiMathAbs(LMathAbs* instr);
 
   // Support for recording safepoint and position information.
   void RecordSafepoint(LPointerMap* pointers,
                        Safepoint::Kind kind,
                        int arguments,
                        Safepoint::DeoptMode mode);
   void RecordSafepoint(LPointerMap* pointers, Safepoint::DeoptMode mode);
   void RecordSafepoint(Safepoint::DeoptMode mode);
@@ skipping 144 matching lines @@
   Label entry_;
   Label exit_;
   Label done_;
   Label* external_exit_;
   int instruction_index_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_X64_LITHIUM_CODEGEN_X64_H_