Tests for Engine ensuring debug-mode apps are attached on iOS. (#37043)

This PR contains the tests for flutter/engine#10186.

dev/devicelab/bin/tasks/system_debug_ios.dart

diff --git a/dev/devicelab/bin/tasks/system_debug_ios.dart b/dev/devicelab/bin/tasks/system_debug_ios.dart
new file mode 100644
index 0000000..aabaca3
--- /dev/null
+++ b/dev/devicelab/bin/tasks/system_debug_ios.dart
@@ -0,0 +1,92 @@
+// Copyright 2019 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:async';
+import 'dart:io';
+
+import 'package:flutter_devicelab/framework/adb.dart';
+import 'package:flutter_devicelab/framework/framework.dart';
+import 'package:flutter_devicelab/framework/ios.dart';
+import 'package:flutter_devicelab/framework/utils.dart';
+
+import 'service_extensions_test.dart';
+
+Future<void> main() async {
+  deviceOperatingSystem = DeviceOperatingSystem.ios;
+  await task(() async {
+    final Device device = await devices.workingDevice;
+    await device.unlock();
+    final String deviceId = device.deviceId;
+
+    final Directory testDirectory =
+        dir('${flutterDirectory.path}/dev/integration_tests/ui');
+    await inDirectory<void>(testDirectory, () async {
+      await flutter('packages', options: <String>['get']);
+      await prepareProvisioningCertificates(testDirectory.path);
+
+      await checkNoWarningHostLaunch(deviceId);
+      await checkNoWarningXcodeLaunch(deviceId);
+      await checkWarningHomeScreenLaunch(deviceId);
+    });
+    return TaskResult.success(<String, dynamic>{});
+  });
+}
+
+const String expectedWarning =
+    'Launching a debug-mode app from the home screen may cause problems.';
+
+// When a debug-mode app is launched from the host there should be no warnings.
+Future<void> checkNoWarningHostLaunch(String deviceId) async {
+  final String output = await evalFlutter('drive', options: <String>[
+    '--debug',
+    '--verbose',
+    '--verbose-system-logs',
+    '-d',
+    deviceId,
+    'lib/empty.dart'
+  ]);
+
+  expect(!output.contains(expectedWarning));
+}
+
+// When a debug-mode app is launched from Xcode there should be no warnings. The
+// Xcode launch is simulated by keeping LLDB attached throughout the lifetime of
+// the app.
+Future<void> checkNoWarningXcodeLaunch(String deviceId) async {
+  await flutter('build',
+      options: <String>['ios', '--debug', '--verbose', 'lib/exit.dart']);
+
+  final String output = await eval(
+      '${flutterDirectory.path}/bin/cache/artifacts/ios-deploy/ios-deploy',
+      <String>[
+        '--bundle',
+        'build/ios/iphoneos/Runner.app',
+        '-d', // Actually start the app in LLDB, don't just install it.
+        '--noninteractive',
+        '--args',
+        '--verbose-logging',
+      ]);
+
+  expect(output.contains('success') && !output.contains(expectedWarning));
+}
+
+// When a debug-mode app is launched from the home screen there should be a
+// warning every ~100 launches. We lower the threshold from to 1 via
+// "--verbose-system-logs" and simulate a home-screen-launch by setting an
+// environment variable. The environment variable forces "flutter drive" to not
+// pass a flag which it normally passes to debug-mode apps, imitating launchd,
+// which doesn't pass any command-line flags.
+Future<void> checkWarningHomeScreenLaunch(String deviceId) async {
+  final String output = await evalFlutter('drive', options: <String>[
+    '--debug',
+    '--verbose',
+    '--verbose-system-logs',
+    '-d',
+    deviceId,
+    'lib/empty.dart'
+  ], environment: <String, String>{
+    'FLUTTER_TOOLS_DEBUG_WITHOUT_CHECKED_MODE': 'true'
+  });
+  expect(output.contains(expectedWarning));
+}
\ No newline at end of file

dev/devicelab/manifest.yaml

diff --git a/dev/devicelab/manifest.yaml b/dev/devicelab/manifest.yaml
index c9cad44..6e8e026 100644
--- a/dev/devicelab/manifest.yaml
+++ b/dev/devicelab/manifest.yaml
@@ -496,6 +496,14 @@
     required_agent_capabilities: ["mac/ios"]
     timeout_in_minutes: 20
 
+  system_debug_ios:
+    description: >
+      Tests that the Engine correctly initializes the system debugger for debug-mode iOS apps.
+    stage: devicelab_ios
+    required_agent_capabilities: ["mac/ios"]
+    timeout_in_minutes: 10
+    flaky: true
+
   ios_sample_catalog_generator:
     description: >
       Builds sample catalog markdown pages and iOS screenshots