Install Reflect[@@toStringTag]

This normative PR reached consensus in the July 2020 TC39:
https://github.com/tc39/ecma262/pull/2057

Bug: v8:10768
Change-Id: Ibe2affea0447b923435f77de5d3c0233deeb9877
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2327753
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69156}

src/init/bootstrapper.cc

@@ -3606,6 +3606,7 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
     Handle<JSObject> reflect =
         factory->NewJSObject(isolate_->object_function(), AllocationType::kOld);
     JSObject::AddProperty(isolate_, global, reflect_string, reflect, DONT_ENUM);
+    InstallToStringTag(isolate_, reflect, reflect_string);
 
     SimpleInstallFunction(isolate_, reflect, "defineProperty",
                           Builtins::kReflectDefineProperty, 3, true);

test/test262/test262.status

@@ -551,9 +551,6 @@
   'built-ins/Atomics/xor/bigint/non-shared-bufferdata': [FAIL],
   'built-ins/Atomics/xor/non-shared-bufferdata': [FAIL],
 
-  # https://bugs.chromium.org/p/v8/issues/detail?id=10768
-  'built-ins/Reflect/Symbol.toStringTag': [FAIL],
-
   # https://bugs.chromium.org/p/v8/issues/detail?id=10769
   'language/expressions/template-literal/invalid-legacy-octal-escape-sequence-8': [FAIL],
   'language/literals/string/legacy-non-octal-escape-sequence-8-strict': [FAIL],