Avoid using a register for constant external array indices.

src/ia32/lithium-ia32.cc

Index: src/ia32/lithium-ia32.cc
diff --git a/src/ia32/lithium-ia32.cc b/src/ia32/lithium-ia32.cc
index 18c6480d89c84bc4e353a04e6542180a739558c8..424163b387110a63e2b7d2487a7c5c275067135c 100644
--- a/src/ia32/lithium-ia32.cc
+++ b/src/ia32/lithium-ia32.cc
@@ -1895,7 +1895,7 @@ LInstruction* LChunkBuilder::DoLoadKeyedSpecializedArrayElement(
                                      array_type == kExternalDoubleArray)));
   ASSERT(instr->key()->representation().IsInteger32());
   LOperand* external_pointer = UseRegister(instr->external_pointer());
-  LOperand* key = UseRegister(instr->key());
+  LOperand* key = UseRegisterOrConstant(instr->key());
   LLoadKeyedSpecializedArrayElement* result =
       new LLoadKeyedSpecializedArrayElement(external_pointer,
                                             key);
@@ -1950,7 +1950,7 @@ LInstruction* LChunkBuilder::DoStoreKeyedSpecializedArrayElement(
   ASSERT(instr->key()->representation().IsInteger32());
 
   LOperand* external_pointer = UseRegister(instr->external_pointer());
-  LOperand* key = UseRegister(instr->key());
+  LOperand* key = UseRegisterOrConstant(instr->key());
   LOperand* temp = NULL;
 
   if (array_type == kExternalPixelArray) {