Fix type checks and display for JS interop types.

pkg/dev_compiler/test/browser/language_tests.js

Index: pkg/dev_compiler/test/browser/language_tests.js
diff --git a/pkg/dev_compiler/test/browser/language_tests.js b/pkg/dev_compiler/test/browser/language_tests.js
index 010334fa617e1eecb2721b169db852d8b92cc1fb..b73ecac150c7ff23962f45a8264d6d07fb2ec339 100644
--- a/pkg/dev_compiler/test/browser/language_tests.js
+++ b/pkg/dev_compiler/test/browser/language_tests.js
@@ -414,9 +414,12 @@ define(['dart_sdk', 'async_helper', 'expect', 'unittest', 'is', 'require'],
       '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.