Fix swarm sample.

This started breaking with some stricter override checks added in 48a258a4a5

Change-Id: I8c1ca90e1edfe7866949e0493db6bc7cc0063e9d
Reviewed-on: https://dart-review.googlesource.com/65783
Reviewed-by: Jacob Richman <jacobr@google.com>
Commit-Queue: Sigmund Cherem <sigmund@google.com>

samples-dev/swarm/swarm_ui_lib/touch/TouchUtil.dart

@@ -239,14 +239,40 @@ class MockTouch implements Touch {
   }
 }
 
+class MockTouchList extends Object
+    with ListMixin<Touch>, ImmutableListMixin<Touch>
+    implements TouchList {
+  final List<Touch> values;
+
+  MockTouchList(this.values);
+
+  static bool get supported => true;
+
+  int get length => values.length;
+
+  Touch operator [](int index) => values[index];
+
+  void operator []=(int index, Touch value) {
+    throw new UnsupportedError("Cannot assign element of immutable List.");
+  }
+
+  set length(int value) {
+    throw new UnsupportedError("Cannot resize immutable List.");
+  }
+
+  Touch item(int index) => values[index];
+}
+
 class MockTouchEvent implements TouchEvent {
   dynamic /*MouseEvent*/ wrapped;
-  // TODO(jacobr): these are currently Lists instead of a TouchList.
-  final List<Touch> touches;
-  final List<Touch> targetTouches;
-  final List<Touch> changedTouches;
-  MockTouchEvent(MouseEvent this.wrapped, List<Touch> this.touches,
-      List<Touch> this.targetTouches, List<Touch> this.changedTouches) {}
+  final TouchList touches;
+  final TouchList targetTouches;
+  final TouchList changedTouches;
+  MockTouchEvent(MouseEvent this.wrapped, List<Touch> touches,
+      List<Touch> targetTouches, List<Touch> changedTouches)
+      : touches = new MockTouchList(touches),
+        targetTouches = new MockTouchList(targetTouches),
+        changedTouches = new MockTouchList(changedTouches);
 
   bool get bubbles => wrapped.bubbles;
 

samples-dev/swarm/swarm_ui_lib/touch/touch.dart

@@ -5,7 +5,13 @@
 library touch;
 
 import 'dart:async';
-import 'dart:collection' show Queue, DoubleLinkedQueue, DoubleLinkedQueueEntry;
+import 'dart:collection'
+    show
+        Queue,
+        DoubleLinkedQueue,
+        DoubleLinkedQueueEntry,
+        ListMixin,
+        ImmutableListMixin;
 import 'dart:html';
 import 'dart:math' as Math;