Require a homepage field in pubspecs.

utils/pub/validator/pubspec_field.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_field_validator;
 
 import '../entrypoint.dart';
 import '../system_cache.dart';
 import '../validator.dart';
 
@@ skipping 25 matching lines @@
               'email address (e.g. "name <email>").');
         }
       }
     }
 
     var homepage = pubspec.fields['homepage'];
     if (homepage == null) {
       errors.add('pubspec.yaml is missing a "homepage" field.');
     }
 
+    var description = pubspec.fields['description'];
+    if (description == null) {
+      errors.add('pubspec.yaml is missing a "description" field.');
+    }
+
     return new Future.immediate(null);
   }
 }