Gracefully handle pubspecs with dependencies using unknown sources.

sdk/lib/_internal/pub/test/lock_file_test.dart

 // Copyright (c) 2012, 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 lock_file_test;
 
 import 'package:unittest/unittest.dart';
 import 'package:yaml/yaml.dart';
 
 import '../lib/src/lock_file.dart';
@@ skipping 47 matching lines @@
     version: 2.3.4
     source: mock
     description: foo desc
 ''', sources);
 
         expect(lockFile.packages.length, equals(2));
 
         var bar = lockFile.packages['bar'];
         expect(bar.name, equals('bar'));
         expect(bar.version, equals(new Version(1, 2, 3)));
-        expect(bar.source, equals(mockSource));
+        expect(bar.source, equals(mockSource.name));
         expect(bar.description, equals('bar desc'));
 
         var foo = lockFile.packages['foo'];
         expect(foo.name, equals('foo'));
         expect(foo.version, equals(new Version(2, 3, 4)));
-        expect(foo.source, equals(mockSource));
+        expect(foo.source, equals(mockSource.name));
         expect(foo.description, equals('foo desc'));
       });
 
       test("throws if the version is missing", () {
         expect(() {
           new LockFile.parse('''
 packages:
   foo:
     source: mock
     description: foo desc
@@ skipping 74 matching lines @@
     });
 
     group('serialize()', () {
       var lockfile;
       setUp(() {
         lockfile = new LockFile.empty();
       });
 
       test('dumps the lockfile to YAML', () {
         lockfile.packages['foo'] = new PackageId(
-            'foo', mockSource, new Version.parse('1.2.3'), 'foo desc');
+            'foo', mockSource.name, new Version.parse('1.2.3'), 'foo desc');
         lockfile.packages['bar'] = new PackageId(
-            'bar', mockSource, new Version.parse('3.2.1'), 'bar desc');
+            'bar', mockSource.name, new Version.parse('3.2.1'), 'bar desc');
 
         expect(loadYaml(lockfile.serialize()), equals({
           'packages': {
             'foo': {
               'version': '1.2.3',
               'source': 'mock',
               'description': 'foo desc'
             },
             'bar': {
               'version': '3.2.1',
               'source': 'mock',
               'description': 'bar desc'
             }
           }
         }));
       });
 
       test('lockfile is alphabetized by package name', () {
         var testNames = ['baz', 'Qwe', 'Q', 'B', 'Bar', 'bar', 'foo'];
         testNames.forEach((name) {
-          lockfile.packages[name] = new PackageId(name, mockSource,
+          lockfile.packages[name] = new PackageId(name, mockSource.name,
             new Version.parse('5.5.5'), '$name desc');
         });
 
         expect(lockfile.serialize(),
           '# Generated by pub\n'
           '# See http://pub.dartlang.org/doc/glossary.html#lockfile\n'
           '\n'
           '{"packages":{'
           '"B":{"version":"5.5.5","source":"mock","description":"B desc"},'
           '"Bar":{"version":"5.5.5","source":"mock","description":"Bar desc"},'
           '"Q":{"version":"5.5.5","source":"mock","description":"Q desc"},'
           '"Qwe":{"version":"5.5.5","source":"mock","description":"Qwe desc"},'
           '"bar":{"version":"5.5.5","source":"mock","description":"bar desc"},'
           '"baz":{"version":"5.5.5","source":"mock","description":"baz desc"},'
           '"foo":{"version":"5.5.5","source":"mock","description":"foo desc"}}}'
           '\n'
         );
       });
     });
   });
 }