Add support for iOS Simulator in `flutter emulators`

packages/flutter_tools/lib/src/emulator.dart

@@ -8,6 +8,7 @@ import 'dart:math' as math;
 import 'android/android_emulator.dart';
 import 'base/context.dart';
 import 'globals.dart';
+import 'ios/ios_emulators.dart';
 
 EmulatorManager get emulatorManager => context[EmulatorManager];
 
@@ -18,6 +19,7 @@ class EmulatorManager {
   EmulatorManager() {
     // Register the known discoverers.
     _emulatorDiscoverers.add(new AndroidEmulators());
+    _emulatorDiscoverers.add(new IOSEmulators());
   }
 
   final List<EmulatorDiscovery> _emulatorDiscoverers = <EmulatorDiscovery>[];

packages/flutter_tools/lib/src/ios/ios_emulators.dart

+// Copyright 2018 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 '../base/file_system.dart';
+import '../base/logger.dart';
+import '../base/platform.dart';
+import '../base/process.dart';
+import '../emulator.dart';
+import '../globals.dart';
+import 'ios_workflow.dart';
+
+// TODO: Is there a better name for this? We already have IOSSimulator classes
+// that represent *running* simulators, but this is about "unlaunched images"...
+class IOSEmulators extends EmulatorDiscovery {
+  @override
+  bool get supportsPlatform => platform.isMacOS;
+
+  @override
+  bool get canListAnything => iosWorkflow.canListEmulators;
+
+  @override
+  Future<List<Emulator>> get emulators async => getEmulators();
+}
+
+class IOSEmulator extends Emulator {
+  IOSEmulator(String id) : super(id, true);
+
+  @override
+  String get name => 'iOS Simulator';
+
+  @override
+  String get manufacturer => 'Apple';
+
+  @override
+  String get label => '';
+
+  @override
+  Future<bool> launch() async {
+    final Status status = logger.startProgress('Launching $id...');
+    final RunResult launchResult =
+        await runAsync(<String>['open', '-a', getSimulatorPath()]);
+    status.stop();
+    if (launchResult.exitCode != 0) {
+      printError(
+          'Error: iOS simulator failed to launch with exit code ${launchResult.exitCode}');
+      printError('$launchResult');
+      return false;
+    }
+
+    return true;
+  }
+}
+
+/// Return the list of iOS Simulators (there can only be zero or one).
+List<IOSEmulator> getEmulators() {
+  final String simulatorPath = getSimulatorPath();
+  if (simulatorPath == null) {
+    return <IOSEmulator>[];
+  }
+
+  return <IOSEmulator>[new IOSEmulator('apple_ios_simulator')];
+}
+
+String getSimulatorPath() {
+  final List<String> searchPaths = <String>[
+    // TODO: Could this be anywhere else?
+    '/Applications/Xcode.app/Contents/Developer/Applications/Simulator.app',
+  ];
+  return searchPaths.where((String p) => p != null).firstWhere(
+    (String p) => fs.directory(p).existsSync(),
+    orElse: () => null,
+  );
+}