fix errors and warnings in DDC

pkg/dev_compiler/web/stack_trace_mapper.dart

 // Copyright (c) 2017, 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.
 
 /// Standalone utility that manages loading source maps for all Dart scripts
 /// on the page compiled with DDC.
 ///
 /// Example JavaScript usage:
 /// $dartStackTraceUtility.addLoadedListener(function() {
 ///   // All Dart source maps are now loaded. It is now safe to start your
 ///   // Dart application compiled with DDC.
 ///   dart_library.start('your_dart_application');
 /// })
 ///
 /// If $dartStackTraceUtility is set, the dart:core StackTrace class calls
 /// $dartStackTraceUtility.mapper(someJSStackTrace)
 /// to apply source maps.
 ///
 /// This utility can be compiled to JavaScript using Dart2JS while the rest
 /// of the application is compiled with DDC or could be compiled with DDC.
 
 @JS()
 library stack_trace_mapper;
 
-import 'dart:async';
-import 'dart:html';
-
 import 'package:js/js.dart';
 import 'package:path/path.dart' as path;
 import 'package:source_map_stack_trace/source_map_stack_trace.dart';
 import 'package:source_maps/source_maps.dart';
 import 'package:source_span/source_span.dart';
 import 'package:stack_trace/stack_trace.dart';
 
 typedef void ReadyCallback();
 
 /// Global object DDC uses to see if a stack trace utility has been registered.
 @JS(r'$dartStackTraceUtility')
 external set dartStackTraceUtility(DartStackTraceUtility value);
 
 typedef String StackTraceMapper(String stackTrace);
 typedef dynamic SourceMapProvider(String modulePath);
-typedef String SetSourceMapProvider(SourceMapProvider provider);
+typedef void SetSourceMapProvider(SourceMapProvider provider);
 
 @JS()
 @anonymous
 class DartStackTraceUtility {
   external factory DartStackTraceUtility(
       {StackTraceMapper mapper, SetSourceMapProvider setSourceMapProvider});
 }
 
 @JS('JSON.stringify')
 external String _stringify(dynamic json);
@@ skipping 35 matching lines @@
     var span = _bundle.spanFor(line, column, files: files, uri: uri);
     // TODO(jacobr): we shouldn't have to filter out invalid sourceUrl entries
     // here.
     if (span == null || span.start.sourceUrl == null) return null;
     var pathSegments = span.start.sourceUrl.pathSegments;
     if (pathSegments.isNotEmpty && pathSegments.last == 'null') return null;
     return span;
   }
 }
 
-String _toSourceMapLocation(String url) {
-  // The url may have cache busting query parameters which we need to maintain
-  // in the source map url.
-  // For example:
-  //   http://localhost/foo.js?cachebusting=23419
-  // Should get source map
-  //   http://localhost/foo.js.map?cachebusting=23419
-  var uri = Uri.parse(url);
-  return uri.replace(path: '${uri.path}.map').toString();
-}
-
 LazyMapping _mapping;
 
 String mapper(String rawStackTrace) {
   if (_mapping == null) {
     // This should not happen if the user has waited for the ReadyCallback
     // to start the application.
     throw new StateError('Source maps are not done loading.');
   }
   return mapStackTrace(_mapping, new Trace.parse(rawStackTrace)).toString();
 }
 
-void setSourceMapProvider(SourceMapProvider provider) async {
+void setSourceMapProvider(SourceMapProvider provider) {
   _mapping = new LazyMapping(provider);
 }
 
 main() {
   // Register with DDC.
   dartStackTraceUtility = new DartStackTraceUtility(
       mapper: allowInterop(mapper),
       setSourceMapProvider: allowInterop(setSourceMapProvider));
 }