binding: Add stopwatch

The stopwatch gets replaced with a testable stopwatch from clock/clock
in tests. We need it for the testability of stopwatches with fake
async. The "normal" stopwatch gets used when not testing.

This implementation was inspired by:

  flutter/flutter@bbdeabf

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/model/binding.dart

@@ -113,6 +113,11 @@ abstract class ZulipBinding {
   /// This wraps [url_launcher.closeInAppWebView].
   Future<void> closeInAppWebView();
 
+  /// Provides access to a new stopwatch.
+  ///
+  /// Outside tests, this just calls the [Stopwatch] constructor.
+  Stopwatch stopwatch();
+
   /// Provides device and operating system information,
   /// via package:device_info_plus.
   ///
@@ -360,6 +365,9 @@ class LiveZulipBinding extends ZulipBinding {
     return url_launcher.closeInAppWebView();
   }
 
+  @override
+  Stopwatch stopwatch() => Stopwatch();
+
   @override
   Future<BaseDeviceInfo?> get deviceInfo => _deviceInfo;
   late Future<BaseDeviceInfo?> _deviceInfo;

test/model/binding.dart

@@ -1,5 +1,6 @@
 import 'dart:async';
 
+import 'package:clock/clock.dart';
 import 'package:firebase_core/firebase_core.dart';
 import 'package:firebase_messaging/firebase_messaging.dart';
 import 'package:flutter/foundation.dart';
@@ -209,6 +210,9 @@ class TestZulipBinding extends ZulipBinding {
     _closeInAppWebViewCallCount++;
   }
 
+  @override
+  Stopwatch stopwatch() => clock.stopwatch();
+
   /// The value that `ZulipBinding.instance.deviceInfo` should return.
   BaseDeviceInfo deviceInfoResult = _defaultDeviceInfoResult;
   static const _defaultDeviceInfoResult = AndroidDeviceInfo(sdkInt: 33, release: '13');