Service Workers: Improve object equality assertion errors

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

 /*
  * testharness-helpers contains various useful extensions to testharness.js to
  * allow them to be used across multiple tests before they have been
  * upstreamed. This file is intended to be usable from both document and worker
  * environments, so code should for example not rely on the DOM.
  */
 
 // A testharness test that simplifies testing with promises.
 //
 // * The |func| argument should be a reference to a function that optionally
@@ skipping 85 matching lines @@
         _is_equal(actual[property], expected[property],
                   prefix + '.' + property);
       });
     Object.getOwnPropertyNames(actual).forEach(function(property) {
         assert_own_property(expected, property, prefix);
       });
 
     object_stack.pop();
   }
 
+  function _brand(object) {
+    return Object.prototype.toString.call(object).match(/^\[object (.*)\]$/)[1];
+  }
+
   _is_equal(actual, expected,
-            (description ? description + ' :' : '') + '[object]');
+            (description ? description + ': ' : '') + _brand(actual));
 };
 
 // Equivalent to assert_in_array, but uses a weaker equivalence relation
 // (assert_object_equals) than '==='.
 function assert_object_in_array(actual, expected_array, description) {
   assert_true(expected_array.some(function(element) {
       try {
         assert_object_equals(actual, element);
         return true;
       } catch (e) {
@@ skipping 23 matching lines @@
 // elements as determined by assert_object_equals(). The corresponding elements
 // must occupy corresponding indices in their respective arrays.
 function assert_array_objects_equals(actual, expected, description) {
   assert_true(Array.isArray(actual), description);
   assert_equals(actual.length, expected.length, description);
   actual.forEach(function(value, index) {
       assert_object_equals(value, expected[index],
                            description + ' : object[' + index + ']');
     });
 }