Service Workers: Improve object equality assertion errors

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 7626c94d6153755bb78b78f6ebb8e56bc5412afc..292e5f9953ec30c36731d045f504806c0b0c17bb 100644
--- a/LayoutTests/http/tests/resources/testharness-helpers.js
+++ b/LayoutTests/http/tests/resources/testharness-helpers.js
@@ -103,8 +103,12 @@ self.assert_object_equals = function(actual, expected, description) {
     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