Use elements/types in constants/values

pkg/compiler/lib/src/constant_system_dart.dart

Index: pkg/compiler/lib/src/constant_system_dart.dart
diff --git a/pkg/compiler/lib/src/constant_system_dart.dart b/pkg/compiler/lib/src/constant_system_dart.dart
index cc126361c90fc3c5847f0a3526a3bca0e00a99de..7c3ebc103d3ca7fffddf04f862ad9a8a1b0af6e8 100644
--- a/pkg/compiler/lib/src/constant_system_dart.dart
+++ b/pkg/compiler/lib/src/constant_system_dart.dart
@@ -458,10 +458,10 @@ class DartConstantSystem extends ConstantSystem {
     // TODO(johnniwinther): Change the `Type` type to
     // `compiler.commonElements.typeType` and check the backend specific value
     // in [checkConstMapKeysDontOverrideEquals] in 'members.dart'.
-    return new TypeConstantValue(
-        type,
-        compiler.backend.backendClasses.typeImplementation
-            .computeType(compiler.resolution));
+    ResolutionInterfaceType implementationType = compiler
+        .backend.backendClasses.typeImplementation
+        .computeType(compiler.resolution);
+    return new TypeConstantValue(type, implementationType);
   }
 
   @override