Provide source map info for simple async methods.

tests/compiler/dart2js/sourcemaps/html_parts.dart

 // Copyright (c) 2016, 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 sourcemap.html_parts;
 
 import 'sourcemap_html_helper.dart';
 
 class Annotation {
   final id;
@@ skipping 107 matching lines @@
       LineDataFunction getLineData}) {
     return new HtmlPrintContext(
         lineNoWidth: lineNoWidth ?? this.lineNoWidth,
         usePre: usePre ?? this.usePre,
         includeAnnotation: includeAnnotation ?? this.includeAnnotation,
         getAnnotationData: getAnnotationData ?? this.getAnnotationData,
         getLineData: getLineData ?? this.getLineData);
   }
 }
 
-enum HtmlPartKind {
-  CODE,
-  LINE,
-  CONST,
-  NEWLINE,
-  TEXT,
-  TAG,
-  LINE_NUMBER,
-}
+enum HtmlPartKind { CODE, LINE, CONST, NEWLINE, TEXT, TAG, LINE_NUMBER, }
 
 abstract class HtmlPart {
   void printHtmlOn(StringBuffer buffer, HtmlPrintContext context);
 
   HtmlPartKind get kind;
 
   toJson(JsonStrategy strategy);
 
   static HtmlPart fromJson(json, JsonStrategy strategy) {
     if (json is String) {
@@ skipping 335 matching lines @@
 
   Annotation decodeAnnotation(Map json) {
     return new Annotation(json['id'], json['codeOffset'], json['title'],
         data: json['data']);
   }
 
   encodeLineAnnotation(lineAnnotation) => lineAnnotation;
 
   decodeLineAnnotation(json) => json;
 }