dart2js cps: Clean up and avoid processing unreachable code.

pkg/compiler/lib/src/constants/values.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.
 
 library dart2js.constants.values;
 
 import '../common.dart';
 import '../core_types.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart'
@@ skipping 357 matching lines @@
 
   final int hashCode;
 
   // TODO(floitsch): cache StringConstants.
   // TODO(floitsch): compute hashcode without calling toString() on the
   // DartString.
   StringConstantValue(DartString value)
       : this.primitiveValue = value,
         this.hashCode = value.slowToString().hashCode;
 
+  StringConstantValue.fromString(String value)
+      : this(new DartString.literal(value));
+
   bool get isString => true;
 
   DartType getType(CoreTypes types) => types.stringType;
 
   bool operator ==(var other) {
     if (other is !StringConstantValue) return false;
     StringConstantValue otherString = other;
     return hashCode == otherString.hashCode &&
            primitiveValue == otherString.primitiveValue;
   }
@@ skipping 353 matching lines @@
   List<ConstantValue> getDependencies() => const <ConstantValue>[];
 
   @override
   DartType getType(CoreTypes types) => const DynamicType();
 
   @override
   String toStructuredString() => 'NonConstant';
 
   @override
   String unparse() => '>>non-constant<<';
-}
+}