Split parser/listener.dart, parser/class_element_listener.dart and tokens/token.dart into smaller l…

pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart

Index: pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart b/pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart
index 9f6aeb86ce9e079da24d4102efca10b73f3effae..d215de3843d6f21546f41f0878110a6b2ce9a677 100644
--- a/pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend_ast_to_frontend_ast.dart
@@ -12,6 +12,9 @@ import '../elements/elements.dart' as elements;
 import '../resolution/tree_elements.dart' show
     TreeElementMapping;
 import '../tokens/token.dart';
+import '../tokens/token_constants.dart';
+import '../tokens/precedence.dart';
+import '../tokens/precedence_constants.dart';
 import '../tree/tree.dart' as tree;
 import '../util/util.dart';
 import 'backend_ast_nodes.dart';