Extension method support to move us closer to a valid List implementation.

test/dart_codegen/expect/core/list.dart

 part of dart.core;
- abstract class List<E> implements Iterable<E>, EfficientLength {external factory List([int length]);
+ @SupportJsExtensionMethod() @JsPeerInterface(name: 'Array') abstract class List<E> implements Iterable<E>, EfficientLength {external factory List([int length]);
  external factory List.filled(int length, E fill);
  external factory List.from(Iterable elements, {
   bool growable : true}
 );
  factory List.generate(int length, E generator(int index), {
   bool growable : true}
 ) {
   List<E> result;
    if (growable) {
     result = <E> []..length = length;
@@ skipping 27 matching lines @@
  void removeWhere(bool test(E element));
  void retainWhere(bool test(E element));
  List<E> sublist(int start, [int end]);
  Iterable<E> getRange(int start, int end);
  void setRange(int start, int end, Iterable<E> iterable, [int skipCount = 0]);
  void removeRange(int start, int end);
  void fillRange(int start, int end, [E fillValue]);
  void replaceRange(int start, int end, Iterable<E> replacement);
  Map<int, E> asMap();
 }