feat: Implement GlanceNoOpImpl in debug mode

README.md

@@ -4,9 +4,7 @@ An APM library for detecting UI jank in Flutter for mobile (Android/iOS).
 
 **NOTE:** This package is experimental. APIs may change without notice before the stable version 1.0.
 
-`glance` detects UI jank during the build phase and from "external sources", such as `WidgetBindingObserver` callbacks, touch events, and method channel callbacks. These cover most cases that cause UI jank. It works only when you build your application with the `--split-debug-info` option, see https://docs.flutter.dev/deployment/obfuscate#obfuscate-your-app for more detail. 
-
-Run `glance` in release or profile build, as detecting UI jank in debug mode is not meaningful.
+`glance` detects UI jank during the build phase as well as through various callbacks, such as, `WidgetBindingObserver` callbacks, touch events, and method channel callbacks. These cover most cases that cause UI jank. It works only in release or profile builds when your application is built with the [`--split-debug-info` option](https://docs.flutter.dev/deployment/obfuscate#obfuscate-your-app). 
 
 ## Getting Started
 

lib/src/glance.dart

@@ -93,7 +93,7 @@ abstract class Glance {
 
   static Glance? _instance;
   static Glance get instance {
-    _instance ??= GlanceImpl();
+    _instance ??= GlanceImpl.create(kDebugMode);
     return _instance!;
   }
 

lib/src/glance_impl.dart

@@ -11,9 +11,27 @@ import 'package:glance/src/glance.dart';
 import 'package:glance/src/sampler.dart';
 import 'package:meta/meta.dart' show visibleForTesting, internal;
 
+/// No-op implementation of [Glance].
+class GlanceNoOpImpl implements Glance {
+  @override
+  Future<void> end() async {}
+
+  @override
+  Future<void> start(
+      {GlanceConfiguration config = const GlanceConfiguration()}) async {}
+}
+
 /// Implementation of [Glance]
 class GlanceImpl implements Glance {
-  GlanceImpl();
+  static Glance create(bool isNoOp) {
+    if (isNoOp) {
+      return GlanceNoOpImpl();
+    }
+
+    return GlanceImpl._();
+  }
+
+  GlanceImpl._();
 
   @visibleForTesting
   GlanceImpl.forTesting(Sampler sampler) : _sampler = sampler;

test/glance_impl_test.dart

@@ -51,6 +51,18 @@ void main() {
     glance = GlanceImpl.forTesting(sampler);
   });
 
+  group('GlanceImpl.create', () {
+    test('return GlanceImpl', () {
+      final instance = GlanceImpl.create(false);
+      expect(instance, isInstanceOf<GlanceImpl>());
+    });
+
+    test('return GlanceNoOpImpl', () {
+      final instance = GlanceImpl.create(true);
+      expect(instance, isInstanceOf<GlanceNoOpImpl>());
+    });
+  });
+
   group('GlanceWidgetBindingMixin', () {
     test(
       'call onCheckJank when calling traceFunctionCall if it is in SchedulerPhase.idle',