[modules] Make @@toStringTag on namespace objects non-configurable.

See https://github.com/tc39/ecma262/pull/747.

R=adamk@chromium.org
BUG=v8:1569

Review-Url: https://codereview.chromium.org/2603193002
Cr-Commit-Position: refs/heads/master@{#42057}

src/bootstrapper.cc

@@ -2553,7 +2553,7 @@ void Genesis::InitializeGlobal(Handle<JSGlobalObject> global_object,
 
     {  // Install @@toStringTag.
       PropertyAttributes attribs =
-          static_cast<PropertyAttributes>(DONT_ENUM | READ_ONLY);
+          static_cast<PropertyAttributes>(DONT_DELETE | DONT_ENUM | READ_ONLY);
       Descriptor d = Descriptor::DataConstant(
           factory->to_string_tag_symbol(),
           factory->NewStringFromAsciiChecked("Module"), attribs);

test/mjsunit/modules-namespace1.js

@@ -46,10 +46,10 @@ assertSame(foo, foo.foo_again);
 assertTrue(Reflect.has(foo, Symbol.toStringTag));
 assertEquals("string", typeof Reflect.get(foo, Symbol.toStringTag));
 assertEquals(
-    {value: "Module", configurable: true, writable: false, enumerable: false},
+    {value: "Module", configurable: false, writable: false, enumerable: false},
     Reflect.getOwnPropertyDescriptor(foo, Symbol.toStringTag));
-
-// TODO(neis): Clarify spec w.r.t. other symbols.
+// TODO(neis): Spec currently says the next one should return true.
+assertFalse(Reflect.deleteProperty(foo, Symbol.toStringTag));
 
 // Nonexistant properties.
 let nonexistant = ["gaga", 123, Symbol('')];

test/test262/test262.status

@@ -419,6 +419,13 @@
   'language/module-code/namespace/internals/own-property-keys-binding-types': [SKIP],
   'language/module-code/namespace/internals/own-property-keys-sort': [SKIP],
 
+  # Symbol.toString on namespace objects was made non-configurable, tests need
+  # to be updated.
+  'language/module-code/namespace/Symbol.toStringTag': [SKIP],
+
+  # Possible spec bug, see comment in https://github.com/tc39/ecma262/pull/747.
+  'language/module-code/namespace/internals/delete-non-exported': [SKIP],
+
 ######################## NEEDS INVESTIGATION ###########################
 
   # These test failures are specific to the intl402 suite and need investigation