[es6] don't "replace" Object.prototype.toString for --harmony-tostring

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index 2d9a13f19a6bc25a74d301c9e8ce07a58a9fc79e..ac6bade303101f5d9c4e2b1dee58b280a34051f1 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -1689,7 +1689,6 @@ EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_array_includes)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_classes)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_object_literals)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_arrow_functions)
-EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_tostring)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_proxies)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_sloppy)
 EMPTY_INITIALIZE_GLOBAL_FOR_FEATURE(harmony_unicode)
@@ -1760,6 +1759,17 @@ void Genesis::InitializeGlobal_harmony_reflect() {
 }
 
 
+void Genesis::InitializeGlobal_harmony_tostring() {
+  Handle<JSObject> builtins(native_context()->builtins());
+
+  Handle<HeapObject> flag(FLAG_harmony_tostring ? heap()->true_value()
+                                                : heap()->false_value());
+  Runtime::SetObjectProperty(isolate(), builtins,
+                             factory()->harmony_tostring_string(), flag,
+                             STRICT).Assert();
+}
+
+
 Handle<JSFunction> Genesis::InstallInternalArray(
     Handle<JSBuiltinsObject> builtins,
     const char* name,