ES6 symbols: Implement Symbol intrinsic and basic functionality

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 002b7108f6a4f3a58cb98e032acc7eba5135bbbe..2f7c7f89984af10948e559885a8c40d21c9b2b79 100644
--- a/src/x64/lithium-codegen-x64.cc
+++ b/src/x64/lithium-codegen-x64.cc
@@ -5472,7 +5472,13 @@ Condition LCodeGen::EmitTypeofIs(Label* true_label,
       __ CompareRoot(input, Heap::kNullValueRootIndex);
       __ j(equal, true_label);
     }
-    __ CmpObjectType(input, FIRST_NONCALLABLE_SPEC_OBJECT_TYPE, input);
+    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);
+    }
     __ j(below, false_label);
     __ CmpInstanceType(input, LAST_NONCALLABLE_SPEC_OBJECT_TYPE);
     __ j(above, false_label);