Use Feature directly in resolution.

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

 // Copyright (c) 2015, 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.
 
 library dart2js.js_helpers.impact;
 
 import '../common/names.dart' show
     Identifiers;
 import '../compiler.dart' show
     Compiler;
@@ skipping 182 matching lines @@
       staticUses: [
         helpers.assertTest,
         helpers.assertThrow]);
 
   BackendImpact get asyncForIn => new BackendImpact(
       staticUses: [
         helpers.streamIteratorConstructor]);
 
   BackendImpact get stringInterpolation => new BackendImpact(
       staticUses: [
-        helpers.stringInterpolationHelper]);
+        helpers.stringInterpolationHelper],
+      otherImpacts: [
+        needsString('Strings are created.')]);
+
+  BackendImpact get stringJuxtaposition {
+    return needsString('String.concat is used.');
+  }
+
+  // TODO(johnniwinther): Point to to the JavaScript classes instead of the Dart
+  // classes in these impacts.
+  BackendImpact get nullLiteral => new BackendImpact(
+      instantiatedClasses: [
+        coreClasses.nullClass]);
+
+  BackendImpact get boolLiteral => new BackendImpact(
+      instantiatedClasses: [
+        coreClasses.boolClass]);
+
+  BackendImpact get intLiteral => new BackendImpact(
+      instantiatedClasses: [
+        coreClasses.intClass]);
+
+  BackendImpact get doubleLiteral => new BackendImpact(
+      instantiatedClasses: [
+        coreClasses.doubleClass]);
+
+  BackendImpact get stringLiteral => new BackendImpact(
+      instantiatedClasses: [
+        coreClasses.stringClass]);
 
   BackendImpact get catchStatement => new BackendImpact(
       staticUses: [
         helpers.exceptionUnwrapper],
       instantiatedClasses: [
         helpers.jsPlainJavaScriptObjectClass,
         helpers.jsUnknownJavaScriptObjectClass]);
 
   BackendImpact get throwExpression => new BackendImpact(
       // We don't know ahead of time whether we will need the throw in a
@@ skipping 84 matching lines @@
       staticUses: [
         // We will neeed to add the "$is" and "$as" properties on the
         // JavaScript object prototype, so we make sure
         // [:defineProperty:] is compiled.
         helpers.defineProperty]);
 
   BackendImpact get closure => new BackendImpact(
       instantiatedClasses: [
         coreClasses.functionClass]);
 }