Fix source information positions for deserialized patched elements.

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 318 matching lines @@
 
   js.Fun compileToJavaScript(
       CodegenWorkItem work, tree_ir.FunctionDefinition definition) {
     CodeGenerator codeGen = new CodeGenerator(glue, work.registry);
     Element element = work.element;
     js.Fun code = codeGen.buildFunction(definition);
     if (element is FunctionElement && element.asyncMarker != AsyncMarker.SYNC) {
       code = backend.rewriteAsync(element, code);
       work.registry.registerAsyncMarker(element);
     }
-    return attachPosition(code, element);
+    return attachPosition(code, work.resolvedAst);
   }
 
   Iterable<CompilerTask> get tasks {
     return <CompilerTask>[
       cpsBuilderTask,
       cpsOptimizationTask,
       treeBuilderTask,
       treeOptimizationTask
     ]..addAll(fallbackCompiler.tasks);
   }
 
-  js.Node attachPosition(js.Node node, AstElement element) {
+  js.Node attachPosition(js.Node node, ResolvedAst resolvedAst) {
     return node.withSourceInformation(sourceInformationFactory
-        .createBuilderForContext(element)
-        .buildDeclaration(backend.frontend.getResolvedAst(element)));
+        .createBuilderForContext(resolvedAst)
+        .buildDeclaration(resolvedAst));
   }
 }