Test new Web IDL class string behavior

WebIDL/ecmascript-binding/class-string.any.js

@@ -0,0 +1,62 @@
+"use strict";
+
+test(() => {
+  assert_own_property(Blob.prototype, Symbol.toStringTag);
+
+  const propDesc = Object.getOwnPropertyDescriptor(Blob.prototype, Symbol.toStringTag);
+  assert_equals(propDesc.value, "Blob", "value");
+  assert_equals(propDesc.configurable, true, "configurable");
+  assert_equals(propDesc.enumerable, false, "enumerable");
+  assert_equals(propDesc.writable, false, "writable");
+}, "@@toStringTag exists on the prototype with the appropriate descriptor");
+
+test(() => {
+  assert_not_own_property(new Blob(), Symbol.toStringTag);
+}, "@@toStringTag must not exist on the instance");
+
+test(() => {
+  assert_equals(Object.prototype.toString.call(Blob.prototype), "[object Blob]");
+}, "Object.prototype.toString applied to the prototype");
+
+test(() => {
+  assert_equals(Object.prototype.toString.call(new Blob()), "[object Blob]");
+}, "Object.prototype.toString applied to an instance");
+
+test(t => {
+  assert_own_property(Blob.prototype, Symbol.toStringTag, "Precondition for this test: @@toStringTag on the prototype");
+
+  t.add_cleanup(() => {
+    Object.defineProperty(Blob.prototype, Symbol.toStringTag, { value: "Blob" });
+  });
+
+  Object.defineProperty(Blob.prototype, Symbol.toStringTag, { value: "NotABlob" });
+  assert_equals(Object.prototype.toString.call(Blob.prototype), "[object NotABlob]", "prototype");
+  assert_equals(Object.prototype.toString.call(new Blob()), "[object NotABlob]", "instance");
+}, "Object.prototype.toString applied after modifying the prototype's @@toStringTag");
+
+test(t => {
+  const instance = new Blob();
+  assert_not_own_property(instance, Symbol.toStringTag, "Precondition for this test: no @@toStringTag on the instance");
+
+  Object.defineProperty(instance, Symbol.toStringTag, { value: "NotABlob" });
+  assert_equals(Object.prototype.toString.call(instance), "[object NotABlob]");
+}, "Object.prototype.toString applied to the instance after modifying the instance's @@toStringTag");
+
+// Chrome had a bug (https://bugs.chromium.org/p/chromium/issues/detail?id=793406) where if there
+// was no @@toStringTag in the prototype, it would fall back to a magic class string. This tests
+// that the bug is fixed.
+
+test(() => {
+  const instance = new Blob();
+  Object.setPrototypeOf(instance, null);
+
+  assert_equals(Object.prototype.toString.call(instance), "[object Object]");
+}, "Object.prototype.toString applied to a null-prototype instance");
+
+// This test must be last.
+test(() => {
+  delete Blob.prototype[Symbol.toStringTag];
+
+  assert_equals(Object.prototype.toString.call(Blob.prototype), "[object Object]", "prototype");
+  assert_equals(Object.prototype.toString.call(new Blob()), "[object Object]", "instance");
+}, "Object.prototype.toString applied after deleting @@toStringTag");

WebIDL/ecmascript-binding/interface-prototype-object.html

@@ -5,18 +5,6 @@
 <script src="/resources/testharness.js"></script>
 <script src="/resources/testharnessreport.js"></script>
 <script>
-// A specification issue was raised for this behavior.
-// https://www.w3.org/Bugs/Public/show_bug.cgi?id=28244
-test(function() {
-  // Checks toString() behavior.
-  assert_class_string(Document.prototype, "DocumentPrototype");
-
-  assert_true(Document.prototype.hasOwnProperty(Symbol.toStringTag),
-              "An interface prototype object should have toStringTag property.");
-  assert_equals(Document.prototype[Symbol.toStringTag], "DocumentPrototype");
-}, "The class string of an interface prototype object is the concatenation of " +
-   "the interface's identifier and the string 'Prototype'.");
-
 test(function() {
   // https://heycam.github.io/webidl/#create-an-interface-prototype-object
   assert_own_property(Element.prototype, Symbol.unscopables, "Element.prototype has @@unscopables.");