pub: treat a pubspec with just comments as empty

dart/utils/tests/pub/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('../../../lib/unittest/unittest.dart');
 #import('../../pub/pubspec.dart');
 #import('../../pub/source.dart');
 #import('../../pub/source_registry.dart');
@@ skipping 35 matching lines @@
         sources.register(new MockSource());
 
         throwsBadFormat(() {
         new Pubspec.parse('''
 dependencies:
   foo:
     mock: bad
 ''', sources);
         });
       });
+
+      test("allows comment-only files", () {
+        var sources = new SourceRegistry();
+        sources.register(new MockSource());
+
+        var pubspec = new Pubspec.parse('''
+# No external dependencies yet
+# Including for completeness
+# ...and hoping the spec expands to include details about author, version, etc
+# See http://www.dartlang.org/docs/pub-package-manager/ for details
+''', sources);
+        expect(pubspec.version, equals(Version.none));
+        expect(pubspec.dependencies, isEmpty);
+      });
     });
   });
 }
 
 throwsBadFormat(function) {
   expectThrow(function, (e) => e is FormatException);
 }