Fix three strong mode analysis issues.

lib/src/version_union.dart

 // Copyright (c) 2015, 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 pub_semver.src.version_union;
 
 import 'package:collection/collection.dart';
 
 import 'utils.dart';
 import 'version.dart';
@@ skipping 41 matching lines @@
     // Only allow Versions and VersionRanges here so we can more easily reason
     // about everything in [flattened]. _EmptyVersions and VersionUnions are
     // filtered out above.
     for (var constraint in flattened) {
       if (constraint is VersionRange) continue;
       throw new ArgumentError('Unknown VersionConstraint type $constraint.');
     }
 
     (flattened as List).sort(compareMax);
 
-    var merged = [];
+    var merged = <VersionRange>[];
     for (var constraint in flattened) {
       // Merge this constraint with the previous one, but only if they touch.
       if (merged.isEmpty ||
           (!merged.last.allowsAny(constraint) &&
               !areAdjacent(merged.last, constraint))) {
         merged.add(constraint);
       } else {
         merged[merged.length - 1] = merged.last.union(constraint);
       }
     }
@@ skipping 52 matching lines @@
 
     return false;
   }
 
   VersionConstraint intersect(VersionConstraint other) {
     var ourConstraints = constraints.iterator;
     var theirConstraints = _constraintsFor(other).iterator;
 
     // Because both lists of constraints are ordered by minimum version, we can
     // safely move through them linearly here.
-    var newConstraints = [];
+    var newConstraints = <VersionRange>[];
     ourConstraints.moveNext();
     theirConstraints.moveNext();
     while (ourConstraints.current != null && theirConstraints.current != null) {
       var intersection = ourConstraints.current
           .intersect(theirConstraints.current);
 
       if (!intersection.isEmpty) newConstraints.add(intersection);
 
       // Move the constraint with the higher max value forward. This ensures
       // that we keep both lists in sync as much as possible, and that large
@@ skipping 27 matching lines @@
 
   bool operator ==(other) {
     if (other is! VersionUnion) return false;
     return const ListEquality().equals(constraints, other.constraints);
   }
 
   int get hashCode => const ListEquality().hash(constraints);
 
   String toString() => constraints.join(" or ");
 }