Implement Harmony semantics for typeof null (behind a flag).

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 ce6a9105f23abac7e1edf923ed559227e7692041..99f84b509bf1d7daf53e60c3de265cd30bfbcbd4 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -4008,6 +4008,10 @@ Condition LCodeGen::EmitTypeofIs(Label* true_label,
     __ CompareRoot(input, Heap::kFalseValueRootIndex);
     final_branch_condition = equal;
 
+  } else if (FLAG_harmony_typeof && type_name->Equals(heap()->null_symbol())) {
+    __ CompareRoot(input, Heap::kNullValueRootIndex);
+    final_branch_condition = equal;
+
   } else if (type_name->Equals(heap()->undefined_symbol())) {
     __ CompareRoot(input, Heap::kUndefinedValueRootIndex);
     __ j(equal, true_label);
@@ -4025,8 +4029,10 @@ Condition LCodeGen::EmitTypeofIs(Label* true_label,
 
   } else if (type_name->Equals(heap()->object_symbol())) {
     __ JumpIfSmi(input, false_label);
-    __ CompareRoot(input, Heap::kNullValueRootIndex);
-    __ j(equal, true_label);
+    if (!FLAG_harmony_typeof) {
+      __ CompareRoot(input, Heap::kNullValueRootIndex);
+      __ j(equal, true_label);
+    }
     __ CmpObjectType(input, FIRST_NONCALLABLE_SPEC_OBJECT_TYPE, input);
     __ j(below, false_label);
     __ CmpInstanceType(input, LAST_NONCALLABLE_SPEC_OBJECT_TYPE);