Make the exit code for dartanalyzer more deterministic.

pkg/analyzer_cli/test/driver_test.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.test.driver;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analyzer/error/error.dart';
@@ skipping 48 matching lines @@
     group('options', () {
       test('todos', () async {
         await drive('data/file_with_todo.dart');
         expect(outSink.toString().contains('[info]'), isFalse);
       });
     });
 
     group('exit codes', () {
       test('fatal hints', () async {
         await drive('data/file_with_hint.dart', args: ['--fatal-hints']);
-        expect(exitCode, 3);
+        expect(exitCode, 1);
       });
 
       test('not fatal hints', () async {
         await drive('data/file_with_hint.dart');
         expect(exitCode, 0);
       });
 
       test('fatal errors', () async {
         await drive('data/file_with_error.dart');
         expect(exitCode, 3);
       });
 
       test('not fatal warnings', () async {
         await drive('data/file_with_warning.dart');
         expect(exitCode, 0);
       });
 
       test('fatal warnings', () async {
         await drive('data/file_with_warning.dart', args: ['--fatal-warnings']);
-        expect(exitCode, 3);
+        expect(exitCode, 2);
       });
 
       test('not parse enableAssertInitializer', () async {
         await drive('data/file_with_assert_initializers.dart',
             args: ['--enable-assert-initializers']);
         expect(exitCode, 0);
       });
 
       test('missing options file', () async {
         await drive('data/test_file.dart', options: 'data/NO_OPTIONS_HERE');
@@ skipping 512 matching lines @@
 
 class TestSource implements Source {
   TestSource();
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }
 
 /// Normalize text with bullets.
 String _bulletToDash(item) => '$item'.replaceAll('•', '-');