Move DartObject into the public API

pkg/analyzer/lib/src/dart/element/handle.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.
 
 library analyzer.src.generated.element_handle;
 
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
-import 'package:analyzer/src/generated/constant.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 
 /**
  * A handle to a [ClassElement].
  */
 class ClassElementHandle extends ElementHandle implements ClassElement {
@@ skipping 1060 matching lines @@
   @override
   bool get isPotentiallyMutatedInScope =>
       actualElement.isPotentiallyMutatedInScope;
 
   @override
   bool get isStatic => actualElement.isStatic;
 
   @override
   DartType get type => actualElement.type;
 }