Make the VersionUnion class public.

lib/src/version_range.dart

 // Copyright (c) 2014, 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.
 
 import 'version.dart';
 import 'version_constraint.dart';
 import 'version_union.dart';
 
 /// Constrains versions to a fall within a given range.
 ///
@@ skipping 106 matching lines @@
   bool _equalsWithoutPreRelease(Version version1, Version version2) =>
       version1.major == version2.major &&
           version1.minor == version2.minor &&
           version1.patch == version2.patch;
 
   bool allowsAll(VersionConstraint other) {
     if (other.isEmpty) return true;
     if (other is Version) return allows(other);
 
     if (other is VersionUnion) {
-      return other.constraints.every((constraint) => allowsAll(constraint));
+      return other.ranges.every((constraint) => allowsAll(constraint));
     }
 
     if (other is VersionRange) {
       if (min != null) {
         if (other.min == null) return false;
         if (min > other.min) return false;
         if (min == other.min && !includeMin && other.includeMin) return false;
       }
 
       if (max != null) {
         if (other.max == null) return false;
         if (max < other.max) return false;
         if (max == other.max && !includeMax && other.includeMax) return false;
       }
 
       return true;
     }
 
     throw new ArgumentError('Unknown VersionConstraint type $other.');
   }
 
   bool allowsAny(VersionConstraint other) {
     if (other.isEmpty) return false;
     if (other is Version) return allows(other);
 
     if (other is VersionUnion) {
-      return other.constraints.any((constraint) => allowsAny(constraint));
+      return other.ranges.any((constraint) => allowsAny(constraint));
     }
 
     if (other is VersionRange) {
       // If neither range has a minimum, they'll overlap at some point.
       //
       //     ...     this     ]
       //     ...     other         ]
       if (min == null && other.min == null) return true;
 
       // If this range has a lower minimum than the other range, it overlaps as
@@ skipping 161 matching lines @@
     if (max != null) {
       if (min != null) buffer.write(' ');
       buffer.write(includeMax ? '<=' : '<');
       buffer.write(max);
     }
 
     if (min == null && max == null) buffer.write('any');
     return buffer.toString();
   }
 }