Refactor BackendHelpers to be reusageable with KernelWorldBuilder

pkg/compiler/lib/src/parser/diet_parser_task.dart

Index: pkg/compiler/lib/src/parser/diet_parser_task.dart
diff --git a/pkg/compiler/lib/src/parser/diet_parser_task.dart b/pkg/compiler/lib/src/parser/diet_parser_task.dart
index 6499632c9d4bf305ddd3b525c540a9172d5547cf..b23441fe9568777afdfc3fccad32ebd926ce9179 100644
--- a/pkg/compiler/lib/src/parser/diet_parser_task.dart
+++ b/pkg/compiler/lib/src/parser/diet_parser_task.dart
@@ -15,8 +15,7 @@ import 'package:front_end/src/fasta/parser.dart'
     show Listener, ParserError, TopLevelParser;
 
 class PartialParser extends TopLevelParser {
-  PartialParser(Listener listener)
-      : super(listener);
+  PartialParser(Listener listener) : super(listener);
 
   Token parseFormalParameters(Token token) => skipFormalParameters(token);
 }