Fixes in custom_element.dart: some of the code was broken, fixes needed for

pkg/pkg.status

Index: pkg/pkg.status
diff --git a/pkg/pkg.status b/pkg/pkg.status
index 30f623fe1d1277af7a763b6d0e5f918ae4117123..39837e0aa74bce90f252e9c091155c72bba7ea51 100644
--- a/pkg/pkg.status
+++ b/pkg/pkg.status
@@ -307,14 +307,6 @@ intl/test/message_extraction/message_extraction_test: Pass, Fail # Issue 12930
 source_maps/test/parser_test: Pass, Timeout # Issue 13719: Please triage this failure.
 polymer_expressions/test/bindings_test: Fail, Pass # Issue 14445.
 
-[ $compiler == dartanalyzer ]
-# pkg issue 13944; Missing inherited member 'Observable._mirror'
-custom_element/test/analyzer_test: fail
-
-[ $compiler == dart2analyzer ]
-# pkg issue 13944; Missing inherited members: 'ListChangeRecord.addedCount' and 'ListChangeRecord.removedCount'
-custom_element/test/analyzer_test: fail
-
 [ $compiler == dartanalyzer || $compiler == dart2analyzer ]
 docgen/test/single_library_test: StaticWarning
 http_server/test/http_body_test: StaticWarning