Improve Array.shift() performance for small arrays.

src/x64/lithium-codegen-x64.cc

Index: src/x64/lithium-codegen-x64.cc
diff --git a/src/x64/lithium-codegen-x64.cc b/src/x64/lithium-codegen-x64.cc
index c3dc8ac30ccef168e72aeb536d8b390077124801..0d837eecd8b307af497c05b8552b84f8b84f25a6 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -4400,6 +4400,15 @@ void LCodeGen::DoTransitionElementsKind(LTransitionElementsKind* instr) {
 }
 
 
+void LCodeGen::DoArrayShift(LArrayShift* instr) {
+  ASSERT(ToRegister(instr->context()).is(rsi));
+  ASSERT(ToRegister(instr->object()).is(rax));
+  ASSERT(ToRegister(instr->result()).is(rax));
+  ArrayShiftStub stub(isolate(), instr->hydrogen()->kind());
+  CallCode(stub.GetCode(), RelocInfo::CODE_TARGET, instr);
+}
+
+
 void LCodeGen::DoTrapAllocationMemento(LTrapAllocationMemento* instr) {
   Register object = ToRegister(instr->object());
   Register temp = ToRegister(instr->temp());