Implement tracking and optimizations of packed 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 3ba0cae7ad9c4107d6deaf59d9423577516d91ba..6094dbb94774edecd4f37dc833dc4b46e23c1893 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2012,8 +2012,9 @@ LInstruction* LChunkBuilder::DoStoreKeyedGeneric(HStoreKeyedGeneric* instr) {
 
 LInstruction* LChunkBuilder::DoTransitionElementsKind(
     HTransitionElementsKind* instr) {
-  if (instr->original_map()->elements_kind() == FAST_SMI_ONLY_ELEMENTS &&
-      instr->transitioned_map()->elements_kind() == FAST_ELEMENTS) {
+  ElementsKind from_kind = instr->original_map()->elements_kind();
+  ElementsKind to_kind = instr->transitioned_map()->elements_kind();
+  if (IsSimpleMapChangeTransition(from_kind, to_kind)) {
     LOperand* object = UseRegister(instr->object());
     LOperand* new_map_reg = TempRegister();
     LOperand* temp_reg = TempRegister();