Fix type checks and display for JS interop types.

pkg/dev_compiler/test/browser/language_tests.js

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 define(['dart_sdk', 'async_helper', 'expect', 'unittest', 'is', 'require'],
       function(dart_sdk, async_helper, expect, unittest, is, require) {
   'use strict';
 
   async_helper = async_helper.async_helper;
   let minitest = expect.minitest;
@@ skipping 396 matching lines @@
 
       // This is failing with a range error, I'm guessing because it's looking
       // for a stylesheet and the page has none.
       'css_rule_list_test': 'fail',
 
       'custom_element_method_clash_test': async_unittest,
       'custom_element_name_clash_test': async_unittest,
       'custom_elements_23127_test': async_unittest,
       'custom_elements_test': async_unittest,
 
-      // TODO(jmesserly): investigate the change here; it is likely due to
-      // different reified types affecting the (gigantic) HTML literal
-      'debugger_test': fail, // firefox_fail
+      // Please do not mark this test as fail. If your change breaks this test,
+      // copy and paste the gigantic JSON literal shown in the test output
+      // into debugger_test.dart and then view the diff with your favorite diff
+      // viewing tool to make sure it looks reasonable. Generally it should be
+      // fairly obvious if the changes are reasonable or not.
+      'debugger_test': firefox_fail,
       'element_animate_test': 'unittest',
 
       // https://github.com/dart-lang/sdk/issues/27579.
       'element_classes_test': 'fail',
       'element_classes_svg_test': 'fail',
 
       // Failure: 'Expected 56 to be in the inclusive range [111, 160].'.
       'element_offset_test': 'fail',
 
       'element_test': async_unittest,
@@ skipping 479 matching lines @@
 
     for (let action of unittest_tests) {
       try {
         action();
       } catch (e) {
         console.error("Caught error tying to setup test:", e);
       }
     }
   });
 });