fix ListMixin _filter and sort to work in strong mode

sdk/lib/collection/list.dart

 // Copyright (c) 2013, 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.
 
 part of dart.collection;
 
 /**
  * Abstract implementation of a list.
  *
  * `ListBase` can be used as a base class for implementing the `List` interface.
@@ skipping 256 matching lines @@
   }
 
   void removeWhere(bool test(E element)) {
     _filter(this, test, false);
   }
 
   void retainWhere(bool test(E element)) {
     _filter(this, test, true);
   }
 
-  static void _filter(List source,
-                      bool test(var element),
-                      bool retainMatching) {
-    List retained = [];
+  void _filter(List source, bool test(var element), bool retainMatching) {
+    List<E> retained = <E>[];

[Jennifer Messerly, 2017/02/24 23:23:57]

This change is needed to prevent a cast failure in strong mode when we cast to
List<E>

[Lasse Reichstein Nielsen, 2017/02/25 10:53:15]

Acknowledged.

     int length = source.length;
     for (int i = 0; i < length; i++) {
       var element = source[i];
       if (test(element) == retainMatching) {
         retained.add(element);
       }
       if (length != source.length) {
         throw new ConcurrentModificationError(source);
       }
     }
@@ skipping 11 matching lines @@
     if (length == 0) {
       throw IterableElementError.noElement();
     }
     E result = this[length - 1];
     length--;
     return result;
   }
 
   void sort([int compare(E a, E b)]) {
     if (compare == null) {
-      Sort.sort(this, Comparable.compare);
+      Sort.sort(this, (a, b) => Comparable.compare(a, b));

[Jennifer Messerly, 2017/02/24 23:23:57]

This change is because Comparable.compare requires that the arguments ("a" and
"b") are Comparables, which is not guaranteed statically for a ListMixin<E>.
This will require a runtime downcast here for each item in the list.

[Lasse Reichstein Nielsen, 2017/02/25 10:53:15]

Comparable.compare was always a type hack, so it's not surprising that it's
failing in strong mode.
We can't check that `this is List<Comparable>` because we do want to sort a
List<Object> of ints ... so I guess this is as good as it gets.

I also don't want to change Comparable.compare to take (dynamic,dynamic) as
argument, that's probably too expensive (making every compareTo call dynamic).

Consider adding a static `int _compareAny(a, b) => a.compareTo(b);` and use that
instead of wrapping Comparable.compare for each invocation.

[Jennifer Messerly, 2017/02/27 18:28:08]

good catch, added _compareAny

     } else {
       Sort.sort(this, compare);
     }
   }
 
   void shuffle([Random random]) {
     if (random == null) random = new Random();
     int length = this.length;
     while (length > 1) {
       int pos = random.nextInt(length);
@@ skipping 184 matching lines @@
       for (E element in iterable) {
         this[index++] = element;
       }
     }
   }
 
   Iterable<E> get reversed => new ReversedListIterable<E>(this);
 
   String toString() => IterableBase.iterableToFullString(this, '[', ']');
 }