Respect `machineFormat` in package-mode.

pkg/analyzer_cli/lib/src/package_analyzer.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.package_analyzer;
 
 import 'dart:core' hide Resource;
 import 'dart:io' as io;
 
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 171 matching lines @@
     ErrorFormatter formatter = new ErrorFormatter(
         sink,
         options,
         stats,
         (AnalysisError error) =>
             AnalyzerImpl.processError(error, options, context));
     for (Source source in explicitSources) {
       AnalysisErrorInfo errorInfo = context.getErrors(source);
       formatter.formatErrors([errorInfo]);
     }
-    stats.print(sink);
+    if (!options.machineFormat) {
+      stats.print(sink);
+    }
   }
 }