Un-deprecate some deprecated code and fix a couple of hints

pkg/analyzer/lib/src/generated/constant.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.constant;
 
 import 'package:analyzer/context/declared_variables.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/src/dart/constant/evaluation.dart';
@@ skipping 79 matching lines @@
 /// >   evaluates to a boolean value.
 /// >   </span>
 ///
 /// The values returned by instances of this class are therefore `null` and
 /// instances of the classes `Boolean`, `BigInteger`, `Double`, `String`, and
 /// `DartObject`.
 ///
 /// In addition, this class defines several values that can be returned to
 /// indicate various conditions encountered during evaluation. These are
 /// documented with the static fields that define those values.
-@deprecated
 class ConstantEvaluator {
   /**
    * The source containing the expression(s) that will be evaluated.
    */
   final Source _source;
 
   /**
    * The type provider used to access the known types.
    */
   final TypeProvider _typeProvider;
@@ skipping 17 matching lines @@
     DartObjectImpl result = expression.accept(new ConstantVisitor(
         new ConstantEvaluationEngine(_typeProvider, new DeclaredVariables(),
             typeSystem: _typeSystem),
         errorReporter));
     if (result != null) {
       return EvaluationResult.forValue(result);
     }
     return EvaluationResult.forErrors(errorListener.errors);
   }
 }