Move DualPivotQuicksort from coreimpl to core as _Sort.

lib/core/sort.dart

 // Copyright (c) 2011, 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.
 
+// TODO(ajohnsen): Remove once coreimpl is eliminated.
+/**
+ * WARNING: This method is temporary and will go away soon.
+ */
+void coreSort(List l, int compare(a, b)) => _Sort.sort(l, compare);
+
 /**
  * Dual-Pivot Quicksort algorithm.
  *
  * This class implements the dual-pivot quicksort algorithm as presented in
  * Vladimir Yaroslavskiy's paper.
  *
  * Some improvements have been copied from Android's implementation.
  */
-class DualPivotQuicksort {
+class _Sort {
   // When a list has less then [:_INSERTION_SORT_THRESHOLD:] elements it will
   // be sorted by an insertion sort.
   static const int _INSERTION_SORT_THRESHOLD = 32;
 
   /**
    * Sorts all elements of the given list [:a:] according to the given
    * [:compare:] function.
    *
    * The [:compare:] function takes two arguments [:x:] and [:y:] and returns
    *  -1 if [:x < y:],
@@ skipping 309 matching lines @@
     } else {
       // The second partition looks as follows:
       // [  *  |  >= pivot1 && <= pivot2  | * ]
       //        ^                        ^
       //       less                    great
       // Simply sort it by recursive descent.
       _doSort(a, less, great, compare);
     }
   }
 }