Call addFile() before getErrors() to actually get errors.

pkg/analyzer_cli/lib/src/analyzer_impl.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_cli.src.analyzer_impl;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:io';
 
@@ skipping 114 matching lines @@
     return await _analyze(printMode);
   }
 
   /// Fills [errorInfos] using [sources].
   Future<Null> prepareErrors() async {
     PerformanceTag previous = _prepareErrorsTag.makeCurrent();
     try {
       for (Source source in sources) {
         if (analysisDriver != null) {
           String path = source.fullName;
+          analysisDriver.addFile(path);
           ErrorsResult errorsResult = await analysisDriver.getErrors(path);
           errorInfos.add(new AnalysisErrorInfoImpl(
               errorsResult.errors, errorsResult.lineInfo));
         } else {
           context.computeErrors(source);
           errorInfos.add(context.getErrors(source));
         }
       }
     } finally {
       previous.makeCurrent();
@@ skipping 234 matching lines @@
   }
 
   @override
   void logInformation(String message, [CaughtException exception]) {
     outSink.writeln(message);
     if (exception != null) {
       outSink.writeln(exception);
     }
   }
 }