Derive source information from ResolvedAst.

pkg/compiler/lib/src/js_backend/codegen/task.dart

 // Copyright (c) 2014, 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.
 
 /// Generate code using the cps-based IR pipeline.
 library code_generator_task;
 
 import 'glue.dart';
 import 'codegen.dart';
 import 'unsugar.dart';
@@ skipping 333 matching lines @@
       cpsBuilderTask,
       cpsOptimizationTask,
       treeBuilderTask,
       treeOptimizationTask
     ]..addAll(fallbackCompiler.tasks);
   }
 
   js.Node attachPosition(js.Node node, AstElement element) {
     return node.withSourceInformation(sourceInformationFactory
         .createBuilderForContext(element)
-        .buildDeclaration(element));
+        .buildDeclaration(backend.frontend.getResolvedAst(element)));
   }
 }