Treat pointer cancel events similarly to pointer up events (#3242)

packages/flutter/lib/src/gestures/binding.dart

@@ -61,14 +61,14 @@ abstract class Gesturer extends BindingBase implements HitTestTarget, HitTestabl
       HitTestResult result = new HitTestResult();
       hitTest(result, event.position);
       _hitTests[event.pointer] = result;
-    } else if (event is! PointerUpEvent) {
+    } else if (event is! PointerUpEvent && event is! PointerCancelEvent) {
       assert(event.down == _hitTests.containsKey(event.pointer));
       if (!event.down)
         return; // we currently ignore add, remove, and hover move events
     }
     assert(_hitTests[event.pointer] != null);
     dispatchEvent(event, _hitTests[event.pointer]);
-    if (event is PointerUpEvent) {
+    if (event is PointerUpEvent || event is PointerCancelEvent) {
       assert(_hitTests.containsKey(event.pointer));
       _hitTests.remove(event.pointer);
     }

packages/flutter/test/gestures/gesture_binding_test.dart

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:ui' as ui;
+
+import 'package:flutter/gestures.dart';
+import 'package:flutter/services.dart';
+import 'package:mojo/bindings.dart' as mojo_bindings;
+import 'package:sky_services/pointer/pointer.mojom.dart';
+import 'package:test/test.dart';
+
+typedef void HandleEventCallback(PointerEvent event);
+
+class TestGestureFlutterBinding extends BindingBase with Gesturer {
+  HandleEventCallback callback;
+
+  @override
+  void handleEvent(PointerEvent event, HitTestEntry entry) {
+    if (callback != null)
+      callback(event);
+    super.handleEvent(event, entry);
+  }  
+}
+
+TestGestureFlutterBinding _binding = new TestGestureFlutterBinding();
+
+void ensureTestGesturer() {
+  if (_binding == null)
+    _binding = new TestGestureFlutterBinding();
+  assert(Gesturer.instance != null);
+}
+
+void main() {
+  setUp(ensureTestGesturer);
+
+  test('Pointer tap events', () {
+    mojo_bindings.Encoder encoder = new mojo_bindings.Encoder();
+
+    PointerPacket packet = new PointerPacket();
+    packet.pointers = <Pointer>[new Pointer(), new Pointer()];
+    packet.pointers[0].type = PointerType.down;
+    packet.pointers[0].kind = PointerKind.touch;
+    packet.pointers[1].type = PointerType.up;
+    packet.pointers[1].kind = PointerKind.touch;
+    packet.encode(encoder);
+
+    List<PointerEvent> events = <PointerEvent>[];
+    _binding.callback = (PointerEvent event) => events.add(event);
+
+    ui.window.onPointerPacket(encoder.message.buffer);
+    expect(events[0].runtimeType, equals(PointerDownEvent));
+    expect(events[1].runtimeType, equals(PointerUpEvent));
+  });
+
+  test('Pointer cancel events', () {
+    mojo_bindings.Encoder encoder = new mojo_bindings.Encoder();
+
+    PointerPacket packet = new PointerPacket();
+    packet.pointers = <Pointer>[new Pointer(), new Pointer()];
+    packet.pointers[0].type = PointerType.down;
+    packet.pointers[0].kind = PointerKind.touch;
+    packet.pointers[1].type = PointerType.cancel;
+    packet.pointers[1].kind = PointerKind.touch;
+    packet.encode(encoder);
+
+    List<PointerEvent> events = <PointerEvent>[];
+    _binding.callback = (PointerEvent event) => events.add(event);
+
+    ui.window.onPointerPacket(encoder.message.buffer);
+    expect(events[0].runtimeType, equals(PointerDownEvent));
+    expect(events[1].runtimeType, equals(PointerCancelEvent));
+  });
+}