Remove TestExpectations for crbug.com/502427 + fix tests

LayoutTests/fast/dom/Window/script-tests/window-custom-prototype.js

Index: LayoutTests/fast/dom/Window/script-tests/window-custom-prototype.js
diff --git a/LayoutTests/fast/dom/Window/script-tests/window-custom-prototype.js b/LayoutTests/fast/dom/Window/script-tests/window-custom-prototype.js
index 1ad8ea0104ec47c45557b813542934a060d20b8a..376134324172d5045bf3822be69de747a5a1a586 100644
--- a/LayoutTests/fast/dom/Window/script-tests/window-custom-prototype.js
+++ b/LayoutTests/fast/dom/Window/script-tests/window-custom-prototype.js
@@ -4,15 +4,15 @@ var originalWindowPrototype = __proto__;
 var chainPointingBackToWindow = { __proto__: window };
 var anotherObject = { };
 
-shouldThrow("__proto__ = window; __proto", "'Error: cyclic __proto__ value'");
-shouldThrow("__proto__ = chainPointingBackToWindow; __proto__", "'Error: cyclic __proto__ value'");
+shouldThrow("__proto__ = window; __proto", "'TypeError: Cyclic __proto__ value'");
+shouldThrow("__proto__ = chainPointingBackToWindow; __proto__", "'TypeError: Cyclic __proto__ value'");
 shouldBe("__proto__ = 1; __proto__", "originalWindowPrototype");
 shouldBe("__proto__ = 'a string'; __proto__", "originalWindowPrototype");
 shouldBe("__proto__ = anotherObject; __proto__", "anotherObject");
-shouldThrow("anotherObject.__proto__ = window; __proto__", "'Error: cyclic __proto__ value'");
+shouldThrow("anotherObject.__proto__ = window; __proto__", "'TypeError: Cyclic __proto__ value'");
 shouldBe("__proto__ = 1; __proto__", "anotherObject");
 shouldBe("__proto__ = 'a string'; __proto__", "anotherObject");
 shouldBe("__proto__ = anotherObject; __proto__", "anotherObject");
 shouldBe("__proto__ = originalWindowPrototype; __proto__", "originalWindowPrototype");
 shouldBe("anotherObject.__proto__ = window; anotherObject.__proto__", "window");
-shouldBe("__proto__ = null; __proto__", "null");
+shouldBe("__proto__ = null; window.__proto__", "undefined");