Handle local functions in kernel_impact.

pkg/compiler/lib/src/js_backend/backend_impact.dart

Index: pkg/compiler/lib/src/js_backend/backend_impact.dart
diff --git a/pkg/compiler/lib/src/js_backend/backend_impact.dart b/pkg/compiler/lib/src/js_backend/backend_impact.dart
index 7fb1e9c0a86afaebf7f9fbad8b8e1358a881c134..3ab0227a795e776694fed5d266e48663cb7d470a 100644
--- a/pkg/compiler/lib/src/js_backend/backend_impact.dart
+++ b/pkg/compiler/lib/src/js_backend/backend_impact.dart
@@ -4,10 +4,12 @@
 
 library dart2js.js_helpers.impact;
 
+import '../common/names.dart';
 import '../compiler.dart' show Compiler;
 import '../core_types.dart' show CommonElements;
 import '../dart_types.dart' show InterfaceType;
 import '../elements/elements.dart' show ClassElement, Element;
+import '../universe/selector.dart';
 import 'backend_helpers.dart';
 import 'constant_system_javascript.dart';
 import 'js_backend.dart';
@@ -15,12 +17,14 @@ import 'js_backend.dart';
 /// A set of JavaScript backend dependencies.
 class BackendImpact {
   final List<Element> staticUses;
+  final List<Selector> dynamicUses;
   final List<InterfaceType> instantiatedTypes;
   final List<ClassElement> instantiatedClasses;
   final List<BackendImpact> otherImpacts;
 
   BackendImpact(
       {this.staticUses: const <Element>[],
+      this.dynamicUses: const <Selector>[],
       this.instantiatedTypes: const <InterfaceType>[],
       this.instantiatedClasses: const <ClassElement>[],
       this.otherImpacts: const <BackendImpact>[]});
@@ -359,6 +363,7 @@ class BackendImpacts {
   BackendImpact get stringInterpolation {
     if (_stringInterpolation == null) {
       _stringInterpolation = new BackendImpact(
+          dynamicUses: [Selectors.toString_],
           staticUses: [helpers.stringInterpolationHelper],
           otherImpacts: [_needsString('Strings are created.')]);
     }