Refactor BackendHelpers to be reusageable with KernelWorldBuilder

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

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.parser.partial_elements;
 
 import '../common.dart';
 import '../common/resolution.dart' show ParsingContext, Resolution;
 import '../elements/resolution_types.dart' show ResolutionDynamicType;
 import '../elements/elements.dart'
@@ skipping 22 matching lines @@
 import '../elements/visitor.dart' show ElementVisitor;
 import 'package:front_end/src/fasta/scanner.dart' show Token;
 import 'package:front_end/src/fasta/scanner.dart' as Tokens show EOF_TOKEN;
 import '../tree/tree.dart';
 import 'package:front_end/src/fasta/parser.dart'
     show ClassMemberParser, Listener, Parser, ParserError;
 import 'member_listener.dart' show MemberListener;
 import 'node_listener.dart' show NodeListener;
 
 class ClassElementParser extends ClassMemberParser {
-  ClassElementParser(Listener listener)
-      : super(listener);
+  ClassElementParser(Listener listener) : super(listener);
 
   Token parseFormalParameters(Token token) => skipFormalParameters(token);
 }
 
 abstract class PartialElement implements DeclarationSite {
   Token beginToken;
   Token endToken;
 
   bool hasParseError = false;
 
@@ skipping 323 matching lines @@
     DiagnosticReporter reporter = parsing.reporter;
     reporter.withCurrentElement(this, () {
       parsing.measure(() {
         MemberListener listener = new MemberListener(
             parsing.getScannerOptionsFor(this), reporter, this);
         Parser parser = new ClassElementParser(listener);
         try {
           Token token = parser.parseTopLevelDeclaration(beginToken);
           assert(identical(token, endToken.next));
           cachedNode = listener.popNode();
-          assert(invariant(reporter.spanFromToken(beginToken),
-                  listener.nodes.isEmpty,
-                  message: "Non-empty listener stack: ${listener.nodes}"));
+          assert(invariant(
+              reporter.spanFromToken(beginToken), listener.nodes.isEmpty,
+              message: "Non-empty listener stack: ${listener.nodes}"));
         } on ParserError {
           // TODO(ahe): Often, a ParserError is thrown while parsing the class
           // body. This means that the stack actually contains most of the
           // information synthesized below. Consider rewriting the parser so
           // endClassDeclaration is called before parsing the class body.
           Identifier name = new Identifier(findMyName(beginToken));
           NodeList typeParameters = null;
           Node supertype = null;
           NodeList interfaces = listener.makeNodeList(0, null, null, ",");
           Token extendsKeyword = null;
@@ skipping 50 matching lines @@
       } on ParserError catch (e) {
         partial.hasParseError = true;
         return new ErrorNode(element.position, e.kind, e.arguments);
       }
       Node node = listener.popNode();
       assert(listener.nodes.isEmpty);
       return node;
     });
   });
 }