Improve Array.shift() performance for small arrays.

src/arm64/lithium-arm64.h

Index: src/arm64/lithium-arm64.h
diff --git a/src/arm64/lithium-arm64.h b/src/arm64/lithium-arm64.h
index 3abc388fe1d7a6d5dddd0ff7cf8311905a47b6fb..49cd4743ac8e39b082b2d4f0c3af4e93e93337df 100644
--- a/src/arm64/lithium-arm64.h
+++ b/src/arm64/lithium-arm64.h
@@ -28,6 +28,7 @@ class LCodeGen;
   V(ArgumentsLength)                            \
   V(ArithmeticD)                                \
   V(ArithmeticT)                                \
+  V(ArrayShift)                                 \
   V(BitI)                                       \
   V(BitS)                                       \
   V(BoundsCheck)                                \
@@ -2852,6 +2853,21 @@ class LTransitionElementsKind V8_FINAL : public LTemplateInstruction<0, 2, 2> {
 };
 
 
+class LArrayShift V8_FINAL : public LTemplateInstruction<1, 2, 0> {
+ public:
+  LArrayShift(LOperand* context, LOperand* object) {
+    inputs_[0] = context;
+    inputs_[1] = object;
+  }
+
+  LOperand* context() const { return inputs_[0]; }
+  LOperand* object() const { return inputs_[1]; }
+
+  DECLARE_CONCRETE_INSTRUCTION(ArrayShift, "array-shift")
+  DECLARE_HYDROGEN_ACCESSOR(ArrayShift)
+};
+
+
 class LTrapAllocationMemento V8_FINAL : public LTemplateInstruction<0, 1, 2> {
  public:
   LTrapAllocationMemento(LOperand* object, LOperand* temp1, LOperand* temp2) {