Add ImportElement and ExportElement

tests/compiler/dart2js/tag_mapping_test.dart

Index: tests/compiler/dart2js/tag_mapping_test.dart
diff --git a/tests/compiler/dart2js/tag_mapping_test.dart b/tests/compiler/dart2js/tag_mapping_test.dart
index 04af1fcef6bb65b07fab895a1d334f13e1b2c3bf..ed781f3d7e38dbc94fb45de6dcc0bdd32da9890f 100644
--- a/tests/compiler/dart2js/tag_mapping_test.dart
+++ b/tests/compiler/dart2js/tag_mapping_test.dart
@@ -33,11 +33,11 @@ void main() {
     Expect.isNotNull(mainApp, 'Could not find main.dart library');
     Expect.isNotNull(lib, 'Could not find library.dart library');
 
-    Import tag = mainApp.tags.single;
-    Expect.isNotNull(tag, 'Could not find import tag in $mainApp');
+    ImportElement import = mainApp.imports.single;
+    Expect.isNotNull(import, 'Could not find import tag in $mainApp');
 
     // Test that we can get from the import tag in main.dart to the
     // library element representing library.dart.
-    Expect.identical(lib, mainApp.getLibraryFromTag(tag));
+    Expect.identical(lib, import.importedLibrary);
   }));
 }