Fix source information positions for deserialized patched elements.

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

Index: pkg/compiler/lib/src/js_backend/codegen/task.dart
diff --git a/pkg/compiler/lib/src/js_backend/codegen/task.dart b/pkg/compiler/lib/src/js_backend/codegen/task.dart
index cf21b0b3b925bcead12f35d4d97832f02606962d..c293d5abe17b15d406139f44d4ed3d62c4e7e3be 100644
--- a/pkg/compiler/lib/src/js_backend/codegen/task.dart
+++ b/pkg/compiler/lib/src/js_backend/codegen/task.dart
@@ -336,7 +336,7 @@ class CpsFunctionCompiler implements FunctionCompiler {
       code = backend.rewriteAsync(element, code);
       work.registry.registerAsyncMarker(element);
     }
-    return attachPosition(code, element);
+    return attachPosition(code, work.resolvedAst);
   }
 
   Iterable<CompilerTask> get tasks {
@@ -348,9 +348,9 @@ class CpsFunctionCompiler implements FunctionCompiler {
     ]..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));
   }
 }