Avoid using a register for constant external array indices.

src/ia32/lithium-codegen-ia32.h

Index: src/ia32/lithium-codegen-ia32.h
diff --git a/src/ia32/lithium-codegen-ia32.h b/src/ia32/lithium-codegen-ia32.h
index c7b96e7f06735bc4e438b0b31aa348a582eb206b..6b132653d45bfb96b9eac0ffe83f79ebfae7c396 100644
--- a/src/ia32/lithium-codegen-ia32.h
+++ b/src/ia32/lithium-codegen-ia32.h
@@ -229,6 +229,9 @@ class LCodeGen BASE_EMBEDDED {
   Register ToRegister(int index) const;
   XMMRegister ToDoubleRegister(int index) const;
   int ToInteger32(LConstantOperand* op) const;
+  Operand BuildExternalArrayOperand(LOperand* external_pointer,
+                                    LOperand* key,
+                                    ExternalArrayType array_type);
 
   // Specific math operations - used from DoUnaryMathOperation.
   void EmitIntegerMathAbs(LUnaryMathOperation* instr);