Move pub into sdk/lib/_internal.

sdk/lib/_internal/pub/lib/src/validator/dependency.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 dependency_validator;
 
 import 'dart:async';
 
 import '../entrypoint.dart';
 import '../hosted_source.dart';
@@ skipping 81 matching lines @@
   }
 
   /// Returns the suggested version constraint for a dependency that was tested
   /// against [version].
   String _constraintForVersion(Version version) {
     if (version.major != 0) return '">=$version <${version.major + 1}.0.0"';
     return '">=$version <${version.major}.${version.minor}.'
         '${version.patch + 1}"';
   }
 }