Add SExpression test and share tests between dart2dart and analyzer2dart.

tests/compiler/dart2js/mock_libraries.dart

Index: tests/compiler/dart2js/mock_libraries.dart
diff --git a/tests/compiler/dart2js/mock_libraries.dart b/tests/compiler/dart2js/mock_libraries.dart
index 734db25f3d4169d9a868caa4b8fc70ded0a2f5d6..62f6d988ecd9e3494bdc534e55a4e0d2f7e792a1 100644
--- a/tests/compiler/dart2js/mock_libraries.dart
+++ b/tests/compiler/dart2js/mock_libraries.dart
@@ -22,11 +22,13 @@ String buildLibrarySource(
 
 const Map<String, String> DEFAULT_CORE_LIBRARY = const <String, String>{
   'bool': 'class bool {}',
+  'Comparator': 'abstract class Comparator<T> {}',
   'DateTime': r'''
       class DateTime {
         DateTime(year);
         DateTime.utc(year);
       }''',
+  'deprecated': 'const deprecated = 0;',
   'double': r'''
       abstract class double extends num {
         static var NAN = 0;