Fix typo in error message.

pkg/analyzer/lib/src/generated/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.resolver;
 
 import "dart:math" as math;
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/utilities_collection.dart';
@@ skipping 7951 matching lines @@
     //    visible in the libraries being resolved, which in turn requires that
     //    we have resolved the import directives.
     //
     _buildElementModels();
     LibraryElement coreElement = _coreLibrary.libraryElement;
     if (coreElement == null) {
       throw new AnalysisException("Could not resolve dart:core");
     }
     LibraryElement asyncElement = _asyncLibrary.libraryElement;
     if (asyncElement == null) {
-      throw new AnalysisException("Coulb not resolve dart:async");
+      throw new AnalysisException("Could not resolve dart:async");
     }
     _buildDirectiveModels();
     _typeProvider = new TypeProviderImpl(coreElement, asyncElement);
     _buildEnumMembers();
     _buildTypeAliases();
     _buildTypeHierarchies();
     _buildImplicitConstructors();
     //
     // Perform resolution and type analysis.
     //
@@ skipping 7711 matching lines @@
    * library.
    */
   final HashSet<String> members = new HashSet<String>();
 
   /**
    * Names of resolved or unresolved class members that are read in the
    * library.
    */
   final HashSet<String> readMembers = new HashSet<String>();
 }