Add support for assert statements with messages to the analyzer.

pkg/analyzer/lib/src/generated/incremental_resolver.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 engine.incremental_resolver;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/src/context/cache.dart'
@@ skipping 1371 matching lines @@
   void _verify(AstNode node) {
     LoggingTimer timer = logger.startTimer();
     try {
       RecordingErrorListener errorListener = new RecordingErrorListener();
       ErrorReporter errorReporter = new ErrorReporter(errorListener, _source);
       ErrorVerifier errorVerifier = new ErrorVerifier(
           errorReporter,
           _definingLibrary,
           _typeProvider,
           new InheritanceManager(_definingLibrary),
-          _context.analysisOptions.enableSuperMixins);
+          _context.analysisOptions.enableSuperMixins,
+          _context.analysisOptions.enableAssertMessage);
       if (_resolutionContext.enclosingClassDeclaration != null) {
         errorVerifier.visitClassDeclarationIncrementally(
             _resolutionContext.enclosingClassDeclaration);
       }
       node.accept(errorVerifier);
       _verifyErrors = errorListener.getErrorsForSource(_source);
     } finally {
       timer.stop('verify');
     }
   }
@@ skipping 751 matching lines @@
   @override
   String toString() => name;
 }
 
 class _TokenPair {
   final _TokenDifferenceKind kind;
   final Token oldToken;
   final Token newToken;
   _TokenPair(this.kind, this.oldToken, this.newToken);
 }