Use Feature directly in resolution.

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

 // Copyright (c) 2012, 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.
 
 part of js_backend;
 
 const VERBOSE_OPTIMIZER_HINTS = false;
 
 class JavaScriptItemCompilationContext extends ItemCompilationContext {
   final Set<HInstruction> boundsChecked = new Set<HInstruction>();
@@ skipping 2725 matching lines @@
           break;
         case Feature.LAZY_FIELD:
           registerBackendImpact(transformed, impacts.lazyField);
           break;
         case Feature.STACK_TRACE_IN_CATCH:
           registerBackendImpact(transformed, impacts.stackTraceInCatch);
           break;
         case Feature.STRING_INTERPOLATION:
           registerBackendImpact(transformed, impacts.stringInterpolation);
           break;
+        case Feature.STRING_JUXTAPOSITION:
+          registerBackendImpact(transformed, impacts.stringJuxtaposition);
+          break;
         case Feature.SUPER_NO_SUCH_METHOD:
           registerBackendImpact(transformed, impacts.superNoSuchMethod);
           break;
         case Feature.SYMBOL_CONSTRUCTOR:
           registerBackendImpact(transformed, impacts.symbolConstructor);
           break;
         case Feature.SYNC_FOR_IN:
           registerBackendImpact(transformed, impacts.syncForIn);
           break;
         case Feature.SYNC_STAR:
@@ skipping 93 matching lines @@
       registerBackendImpact(transformed, impacts.closure);
       for (LocalFunctionElement closure in worldImpact.closures) {
         if (closure.computeType(backend.resolution).containsTypeVariables) {
           backend.compiler.enqueuer.resolution.universe
               .closuresWithFreeTypeVariables.add(closure);
           registerBackendImpact(transformed, impacts.computeSignature);
         }
       }
     }
 
+    for (ConstantExpression constant in worldImpact.constantLiterals) {
+      switch (constant.kind) {
+        case ConstantExpressionKind.NULL:
+          registerBackendImpact(transformed, impacts.nullLiteral);
+          break;
+        case ConstantExpressionKind.BOOL:
+          registerBackendImpact(transformed, impacts.boolLiteral);
+          break;
+        case ConstantExpressionKind.INT:
+          registerBackendImpact(transformed, impacts.intLiteral);
+          break;
+        case ConstantExpressionKind.DOUBLE:
+          registerBackendImpact(transformed, impacts.doubleLiteral);
+          break;
+        case ConstantExpressionKind.STRING:
+          registerBackendImpact(transformed, impacts.stringLiteral);
+          break;
+        default:
+          assert(invariant(NO_LOCATION_SPANNABLE, false,
+              message: "Unexpected constant literal: ${constant.kind}."));
+      }
+    }
+
     return transformed;
   }
 
   void registerBackendImpact(TransformedWorldImpact worldImpact,
                              BackendImpact backendImpact) {
     for (Element staticUse in backendImpact.staticUses) {
       assert(staticUse != null);
       backend.registerBackendUse(staticUse);
       worldImpact.registerStaticUse(
           // TODO(johnniwinther): Store the correct use in impacts.
@@ skipping 172 matching lines @@
   }
 }
 
 /// Records that [constant] is used by the element behind [registry].
 class Dependency {
   final ConstantValue constant;
   final Element annotatedElement;
 
   const Dependency(this.constant, this.annotatedElement);
 }