Add test for PointerRouter

packages/unit/test/base/pointer_router_test.dart

+import 'dart:sky' as sky;
+
+import 'package:sky/base/hit_test.dart';
+import 'package:sky/base/pointer_router.dart';
+import 'package:test/test.dart';
+
+class TestPointerEvent extends sky.PointerEvent {
+  TestPointerEvent({ this.pointer });
+
+  final int pointer;
+}
+
+void main() {
+  test('Should route pointers', () {
+    bool callbackRan = false;
+    void callback(sky.PointerEvent event) {
+      callbackRan = true;
+    }
+
+    PointerRouter router = new PointerRouter();
+    router.addRoute(3, callback);
+    expect(router.handleEvent(new TestPointerEvent(pointer: 2), null), equals(EventDisposition.ignored));
+    expect(callbackRan, isFalse);
+    expect(router.handleEvent(new TestPointerEvent(pointer: 3), null), equals(EventDisposition.processed));
+    expect(callbackRan, isTrue);
+    callbackRan = false;
+    router.removeRoute(3, callback);
+    expect(router.handleEvent(new TestPointerEvent(pointer: 3), null), equals(EventDisposition.ignored));
+    expect(callbackRan, isFalse);
+  });
+}