fix ListMixin _filter and sort to work in strong mode

sdk/lib/collection/list.dart

Index: sdk/lib/collection/list.dart
diff --git a/sdk/lib/collection/list.dart b/sdk/lib/collection/list.dart
index b81b8dd7c11fc2180336f577443e4a92fe3b66d7..9c19c1e92baf2b91b44535a00a862f946e26f552 100644
--- a/sdk/lib/collection/list.dart
+++ b/sdk/lib/collection/list.dart
@@ -274,10 +274,8 @@ abstract class ListMixin<E> implements List<E> {
     _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];
@@ -309,7 +307,7 @@ abstract class ListMixin<E> implements List<E> {
 
   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);
     }