Add publishTo to pubspec and use it in pub lish.

sdk/lib/_internal/pub/test/pubspec_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 pubspec_test;
 
 import 'dart:async';
 
 import 'package:unittest/unittest.dart';
 
@@ skipping 395 matching lines @@
             (pubspec) => pubspec.environment);
         expectPubspecException('environment: {sdk: 1.0}',
             (pubspec) => pubspec.environment);
       });
 
       test("throws if the sdk isn't a valid version constraint", () {
         expectPubspecException('environment: {sdk: "oopies"}',
             (pubspec) => pubspec.environment);
       });
     });
+
+    group("publishTo", () {
+      test("defaults to null if omitted", () {
+        var pubspec = new Pubspec.parse('', sources);
+        expect(pubspec.publishTo, isNull);
+      });
+
+      test("throws if not a string", () {
+        expectPubspecException('publishTo: 123',
+            (pubspec) => pubspec.publishTo);
+      });
+
+      test("allows a URL", () {
+        var pubspec = new Pubspec.parse('''
+publishTo: http://example.com
+''', sources);
+        expect(pubspec.publishTo, equals("http://example.com"));
+      });
+
+      test("allows none", () {
+        var pubspec = new Pubspec.parse('''
+publishTo: none
+''', sources);
+        expect(pubspec.publishTo, equals("none"));
+      });
+
+      test("throws on other strings", () {
+        expectPubspecException('publishTo: http://bad.url:not-port',
+            (pubspec) => pubspec.publishTo);
+      });
+    });
   });
 }