Enable messages in asserts by default

pkg/analyzer/lib/src/task/dart.dart

 // Copyright (c) 2015, 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.task.dart;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 6214 matching lines @@
         errorReporter, libraryElement, typeProvider, context.declaredVariables);
     unit.accept(constantVerifier);
     //
     // Use the ErrorVerifier to compute errors.
     //
     ErrorVerifier errorVerifier = new ErrorVerifier(
         errorReporter,
         libraryElement,
         typeProvider,
         new InheritanceManager(libraryElement),
-        context.analysisOptions.enableSuperMixins,
-        context.analysisOptions.enableAssertMessage);
+        context.analysisOptions.enableSuperMixins);
     unit.accept(errorVerifier);
     //
     // Convert the pending errors into actual errors.
     //
     for (PendingError pendingError in pendingErrors) {
       errorListener.onError(pendingError.toAnalysisError());
     }
     //
     // Record outputs.
     //
@@ skipping 241 matching lines @@
 
   @override
   bool moveNext() {
     if (_newSources.isEmpty) {
       return false;
     }
     currentTarget = _newSources.removeLast();
     return true;
   }
 }