MIPS64: Enable shorten-64-to-32 warning.

src/mips64/lithium-codegen-mips64.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_MIPS_LITHIUM_CODEGEN_MIPS_H_
 #define V8_MIPS_LITHIUM_CODEGEN_MIPS_H_
 
 #include "src/deoptimizer.h"
 #include "src/lithium-codegen.h"
 #include "src/mips64/lithium-gap-resolver-mips64.h"
@@ skipping 57 matching lines @@
   // LOperand is loaded into scratch, unless already a register.
   Register EmitLoadRegister(LOperand* op, Register scratch);
 
   // LOperand must be a double register.
   DoubleRegister ToDoubleRegister(LOperand* op) const;
 
   // LOperand is loaded into dbl_scratch, unless already a double register.
   DoubleRegister EmitLoadDoubleRegister(LOperand* op,
                                         FloatRegister flt_scratch,
                                         DoubleRegister dbl_scratch);
-  int32_t ToRepresentation_donotuse(LConstantOperand* op,
+  int64_t ToRepresentation_donotuse(LConstantOperand* op,
                                     const Representation& r) const;
   int32_t ToInteger32(LConstantOperand* op) const;
   Smi* ToSmi(LConstantOperand* op) const;
   double ToDouble(LConstantOperand* op) const;
   Operand ToOperand(LOperand* op);
   MemOperand ToMemOperand(LOperand* op) const;
   // Returns a MemOperand pointing to the high word of a DoubleStackSlot.
   MemOperand ToHighMemOperand(LOperand* op) const;
 
   bool IsInteger32(LConstantOperand* op) const;
@@ skipping 343 matching lines @@
   LCodeGen* codegen_;
   Label entry_;
   Label exit_;
   Label* external_exit_;
   int instruction_index_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_MIPS_LITHIUM_CODEGEN_MIPS_H_