ES6 symbols: turn symbols into a proper primitive type

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 b9bd30bb161bbcec73252dfcb9c7c5c1f216e1d7..0bb676b9dbe12ff0690e7d06e68e0f3660ba83f6 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -5538,6 +5538,11 @@ Condition LCodeGen::EmitTypeofIs(Label* true_label,
              Immediate(1 << Map::kIsUndetectable));
     final_branch_condition = zero;
 
+  } else if (type_name->Equals(heap()->symbol_string())) {
+    __ JumpIfSmi(input, false_label);
+    __ CmpObjectType(input, SYMBOL_TYPE, input);
+    final_branch_condition = equal;
+
   } else if (type_name->Equals(heap()->boolean_string())) {
     __ CompareRoot(input, Heap::kTrueValueRootIndex);
     __ j(equal, true_label);
@@ -5572,13 +5577,7 @@ Condition LCodeGen::EmitTypeofIs(Label* true_label,
       __ CompareRoot(input, Heap::kNullValueRootIndex);
       __ j(equal, true_label);
     }
-    if (FLAG_harmony_symbols) {
-      __ CmpObjectType(input, SYMBOL_TYPE, input);
-      __ j(equal, true_label);
-      __ CmpInstanceType(input, FIRST_NONCALLABLE_SPEC_OBJECT_TYPE);
-    } else {
-      __ CmpObjectType(input, FIRST_NONCALLABLE_SPEC_OBJECT_TYPE, input);
-    }
+    __ CmpObjectType(input, FIRST_NONCALLABLE_SPEC_OBJECT_TYPE, input);
     __ j(below, false_label);
     __ CmpInstanceType(input, LAST_NONCALLABLE_SPEC_OBJECT_TYPE);
     __ j(above, false_label);