Improve Array.shift() performance for small arrays.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index eb9e7dd00a6a79d97563d219db5a70d7afbeb7d8..cbade8a7d95fac4b2309b7e1fd648a3f17ba1454 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2253,6 +2253,14 @@ LInstruction* LChunkBuilder::DoTransitionElementsKind(
 }
 
 
+LInstruction* LChunkBuilder::DoArrayShift(HArrayShift* instr) {
+  LOperand* object = UseFixed(instr->object(), rax);
+  LOperand* context = UseFixed(instr->context(), rsi);
+  LArrayShift* result = new(zone()) LArrayShift(context, object);
+  return MarkAsCall(DefineFixed(result, rax), instr, CANNOT_DEOPTIMIZE_EAGERLY);
+}
+
+
 LInstruction* LChunkBuilder::DoTrapAllocationMemento(
     HTrapAllocationMemento* instr) {
   LOperand* object = UseRegister(instr->object());