Revert "Move dart2jslib parts into separate libraries."

tests/compiler/dart2js/backend_dart/sexpr_unstringifier.dart

 // Copyright (c) 2014, 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.
 
 // SExpressionUnstringifier implements the inverse operation to
 // [SExpressionStringifier].
 
 library sexpr_unstringifier;
 
 import 'package:compiler/src/constants/expressions.dart';
 import 'package:compiler/src/constants/values.dart';
+import 'package:compiler/src/dart2jslib.dart' as dart2js
+    show MessageKind;
 import 'package:compiler/src/dart_types.dart' as dart_types
     show DartType;
 import 'package:compiler/src/elements/elements.dart';
 import 'package:compiler/src/elements/modelx.dart'
     show ErroneousElementX, TypeVariableElementX;
-import 'package:compiler/src/messages.dart'
-    show MessageKind;
 import 'package:compiler/src/tree/tree.dart' show LiteralDartString;
 import 'package:compiler/src/universe/universe.dart'
     show Selector, SelectorKind, CallStructure;
 import 'package:compiler/src/cps_ir/cps_ir_nodes.dart';
 
 /// Used whenever a node constructed by [SExpressionUnstringifier] needs a
 /// named entity.
 class DummyEntity extends Entity {
   final String name;
   DummyEntity(this.name);
@@ skipping 12 matching lines @@
 // that could not be resolved correctly.  Perhaps the IR should not rely on
 // elements at all for naming.
 /// Used whenever a node constructed by [SExpressionUnstringifier] requires
 /// an [Element] or [FunctionElement]. Extends [ErroneousElementX] since there
 /// is currently a large amount of overhead when extending the base abstract
 /// classes, and erroneous elements conveniently also skip several assertion
 /// checks in CPS IR nodes that are irrelevant to us.
 class DummyElement extends ErroneousElementX
     implements TypeVariableElement, FieldElement {
   DummyElement(String name)
-      : super(MessageKind.GENERIC, {}, name, null);
+      : super(dart2js.MessageKind.GENERIC, {}, name, null);
 
   final dart_types.DartType bound = null;
   final TypeDeclarationElement typeDeclaration = null;
 
   noSuchMethod(inv) => super.noSuchMethod(inv);
 }
 
 /// Used whenever a node constructed by [SExpressionUnstringifier] requires
 /// a named type.
 class DummyNamedType extends dart_types.DartType {
@@ skipping 812 matching lines @@
     tokens.consumeStart(SET_FIELD);
 
     Primitive object = name2variable[tokens.read()];
     Element field = new DummyElement(tokens.read());
     Primitive value = name2variable[tokens.read()];
 
     tokens.consumeEnd();
     return new SetField(object, field, value);
   }
 }