fix strong mode messages in pkg/dev_compiler

pkg/dev_compiler/lib/src/compiler/code_generator.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.
 
 import 'dart:collection' show HashMap, HashSet;
 import 'dart:math' show min, max;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart' show Token, TokenType;
@@ skipping 5077 matching lines @@
 
   @override
   visitNode(AstNode node) {
     // TODO(jmesserly): verify this is unreachable.
     throw 'Unimplemented ${node.runtimeType}: $node';
   }
 
   _visit(AstNode node) {
     if (node == null) return null;
     var result = node.accept(this);
-    if (result is JS.Node) result = annotate(result, node);
-    return result;
+    return result is JS.Node ? annotate(result, node) : result;
   }
 
   List/*<T>*/ _visitList/*<T extends AstNode>*/(Iterable/*<T>*/ nodes) {
     if (nodes == null) return null;
     var result = /*<T>*/ [];
     for (var node in nodes) result.add(_visit(node) as dynamic/*=T*/);
     return result;
   }
 
   /// Visits a list of expressions, creating a comma expression if needed in JS.
@@ skipping 342 matching lines @@
 }
 
 bool isLibraryPrefix(Expression node) =>
     node is SimpleIdentifier && node.staticElement is PrefixElement;
 
 LibraryElement _getLibrary(AnalysisContext c, String uri) =>
     c.computeLibraryElement(c.sourceFactory.forUri(uri));
 
 bool _isDartRuntime(LibraryElement l) =>
     l.isInSdk && l.source.uri.toString() == 'dart:_runtime';