bindings: Fixes layouttests when moving attributes to prototype chains.

LayoutTests/http/tests/resources/testharness-helpers.js

Index: LayoutTests/http/tests/resources/testharness-helpers.js
diff --git a/LayoutTests/http/tests/resources/testharness-helpers.js b/LayoutTests/http/tests/resources/testharness-helpers.js
index 7f66fed8091bcc3367b7bbd582679b49fadfcd0a..f1c0c8b56a0cbff0fffbff9597a9d56563551a71 100644
--- a/LayoutTests/http/tests/resources/testharness-helpers.js
+++ b/LayoutTests/http/tests/resources/testharness-helpers.js
@@ -122,3 +122,25 @@ function assert_array_objects_equals(actual, expected, description) {
                            description + ' : object[' + index + ']');
     });
 }
+
+// Asserts that |object| that is an instance of some interface has the attribute
+// |attribute_name| following the conditions specified by WebIDL, but it's
+// acceptable that the attribute |attribute_name| is an own property of the
+// object because we're in the middle of moving the attribute to a prototype
+// chain.  Once we complete the transition to prototype chains,
+// assert_will_be_idl_attribute must be replaced with assert_idl_attribute
+// defined in testharness.js.
+//
+// FIXME: Remove assert_will_be_idl_attribute once we complete the transition
+// of moving the DOM attributes to prototype chains.
+function assert_will_be_idl_attribute(object, attribute_name, description) {
+  assert_true(typeof object === "object", description);
+
+  assert_true("hasOwnProperty" in object, description);
+
+  // Do not test if |attribute_name| is not an own property because
+  // |attribute_name| is in the middle of the transition to a prototype
+  // chain.

[haraken, 2015/01/23 01:41:32]

Add a crbug number.

[Yuki, 2015/01/23 08:06:20]

Done.

+
+  assert_true(attribute_name in object, description);
+}