add --start-paused,--debug-port flags

packages/flutter_tools/lib/src/android/device_android.dart

@@ -9,7 +9,9 @@ import 'package:crypto/crypto.dart';
 import 'package:path/path.dart' as path;
 
 import '../application_package.dart';
+import '../base/common.dart';
 import '../base/context.dart';
+import '../base/os.dart';
 import '../base/process.dart';
 import '../build_configuration.dart';
 import '../device.dart';
@@ -33,8 +35,6 @@ class AndroidDeviceDiscovery extends DeviceDiscovery {
 }
 
 class AndroidDevice extends Device {
-  static const int _observatoryPort = 8181;
-
   static final String defaultDeviceID = 'default_android_device';
 
   String productID;
@@ -240,22 +240,37 @@ class AndroidDevice extends Device {
     return true;
   }
 
-  void _forwardObservatoryPort() {
-    // Set up port forwarding for observatory.
-    String portString = 'tcp:$_observatoryPort';
+  Future _forwardObservatoryPort(int port) async {
+    bool portWasZero = port == 0;
+
+    if (port == 0) {
+      // Auto-bind to a port. Set up forwarding for that port. Emit a stdout
+      // message similar to the command-line VM, so that tools can parse the output.
+      // "Observatory listening on http://127.0.0.1:52111"
+      port = await findAvailablePort();
+    }
+
     try {
-      runCheckedSync(adbCommandForDevice(<String>['forward', portString, portString]));
+      // Set up port forwarding for observatory.
+      runCheckedSync(adbCommandForDevice(<String>[
+        'forward', 'tcp:$port', 'tcp:$observatoryDefaultPort'
+      ]));
+
+      if (portWasZero)
+        printStatus('Observatory listening on http://127.0.0.1:$port');
     } catch (e) {
-      printError('Unable to forward observatory port ($_observatoryPort):\n$e');
+      printError('Unable to forward Observatory port $port: $e');
     }
   }
 
-  bool startBundle(AndroidApk apk, String bundlePath, {
+  Future<bool> startBundle(AndroidApk apk, String bundlePath, {
     bool checked: true,
     bool traceStartup: false,
     String route,
-    bool clearLogs: false
-  }) {
+    bool clearLogs: false,
+    bool startPaused: false,
+    int debugPort: observatoryDefaultPort
+  }) async {
     printTrace('$this startBundle');
 
     if (!FileSystemEntity.isFileSync(bundlePath)) {
@@ -263,7 +278,7 @@ class AndroidDevice extends Device {
       return false;
     }
 
-    _forwardObservatoryPort();
+    await _forwardObservatoryPort(debugPort);
 
     if (clearLogs)
       this.clearLogs();
@@ -280,6 +295,8 @@ class AndroidDevice extends Device {
       cmd.addAll(['--ez', 'enable-checked-mode', 'true']);
     if (traceStartup)
       cmd.addAll(['--ez', 'trace-startup', 'true']);
+    if (startPaused)
+      cmd.addAll(['--ez', 'start-paused', 'true']);
     if (route != null)
       cmd.addAll(['--es', 'route', route]);
     cmd.add(apk.launchActivity);
@@ -295,22 +312,27 @@ class AndroidDevice extends Device {
     String route,
     bool checked: true,
     bool clearLogs: false,
+    bool startPaused: false,
+    int debugPort: observatoryDefaultPort,
     Map<String, dynamic> platformArgs
-  }) {
-    return flx.buildInTempDir(
+  }) async {
+    flx.DirectoryResult buildResult = await flx.buildInTempDir(
       toolchain,
       mainPath: mainPath
-    ).then((flx.DirectoryResult buildResult) {
+    );
+
     printTrace('Starting bundle for $this.');
 
     try {
-        if (startBundle(
+      if (await startBundle(
         package,
         buildResult.localBundlePath,
         checked: checked,
         traceStartup: platformArgs['trace-startup'],
         route: route,
-          clearLogs: clearLogs
+        clearLogs: clearLogs,
+        startPaused: startPaused,
+        debugPort: debugPort
       )) {
         return true;
       } else {
@@ -319,7 +341,6 @@ class AndroidDevice extends Device {
     } finally {
       buildResult.dispose();
     }
-    });
   }
 
   Future<bool> stopApp(ApplicationPackage app) async {

packages/flutter_tools/lib/src/base/common.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.
+
+const int observatoryDefaultPort = 8181;

packages/flutter_tools/lib/src/base/os.dart

@@ -2,6 +2,7 @@
 // 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';
 
 final OperatingSystemUtils os = new OperatingSystemUtils._();
@@ -31,3 +32,10 @@ class _WindowsUtils implements OperatingSystemUtils {
     return new ProcessResult(0, 0, null, null);
   }
 }
+
+Future<int> findAvailablePort() async {
+  ServerSocket socket = await ServerSocket.bind(InternetAddress.LOOPBACK_IP_V4, 0);
+  int port = socket.port;
+  await socket.close();
+  return port;
+}

packages/flutter_tools/lib/src/commands/start.dart

@@ -8,6 +8,7 @@ import 'dart:io';
 import 'package:path/path.dart' as path;
 
 import '../application_package.dart';
+import '../base/common.dart';
 import '../base/context.dart';
 import '../device.dart';
 import '../runner/flutter_command.dart';
@@ -58,6 +59,13 @@ class StartCommand extends StartCommandBase {
     argParser.addFlag('clear-logs',
         defaultsTo: true,
         help: 'Clear log history before starting the app.');
+    argParser.addFlag('start-paused',
+        defaultsTo: false,
+        negatable: false,
+        help: 'Start in a paused mode and wait for a debugger to connect.');
+    argParser.addOption('debug-port',
+        defaultsTo: observatoryDefaultPort.toString(),
+        help: 'Listen to the given port for a debug connection.');
   }
 
   @override
@@ -71,6 +79,15 @@ class StartCommand extends StartCommandBase {
 
     bool clearLogs = argResults['clear-logs'];
 
+    int debugPort;
+
+    try {
+      debugPort = int.parse(argResults['debug-port']);
+    } catch (error) {
+      printError('Invalid port for `--debug-port`: $error');
+      return 1;
+    }
+
     int result = await startApp(
       devices,
       applicationPackages,
@@ -81,7 +98,9 @@ class StartCommand extends StartCommandBase {
       checked: argResults['checked'],
       traceStartup: argResults['trace-startup'],
       route: argResults['route'],
-      clearLogs: clearLogs
+      clearLogs: clearLogs,
+      startPaused: argResults['start-paused'],
+      debugPort: debugPort
     );
 
     printTrace('Finished start command.');
@@ -99,7 +118,9 @@ Future<int> startApp(
   bool checked: true,
   bool traceStartup: false,
   String route,
-  bool clearLogs: false
+  bool clearLogs: false,
+  bool startPaused: false,
+  int debugPort: observatoryDefaultPort
 }) async {
 
   String mainPath = findMainDartFile(target);
@@ -144,6 +165,8 @@ Future<int> startApp(
       route: route,
       checked: checked,
       clearLogs: clearLogs,
+      startPaused: startPaused,
+      debugPort: debugPort,
       platformArgs: platformArgs
     );
 

packages/flutter_tools/lib/src/device.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'android/device_android.dart';
 import 'application_package.dart';
+import 'base/common.dart';
 import 'base/context.dart';
 import 'build_configuration.dart';
 import 'ios/device_ios.dart';
@@ -104,6 +105,8 @@ abstract class Device {
     String route,
     bool checked: true,
     bool clearLogs: false,
+    bool startPaused: false,
+    int debugPort: observatoryDefaultPort,
     Map<String, dynamic> platformArgs
   });
 

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

@@ -8,6 +8,7 @@ import 'dart:io';
 import 'package:path/path.dart' as path;
 
 import '../application_package.dart';
+import '../base/common.dart';
 import '../base/context.dart';
 import '../base/process.dart';
 import '../build_configuration.dart';
@@ -185,9 +186,12 @@ class IOSDevice extends Device {
     String route,
     bool checked: true,
     bool clearLogs: false,
+    bool startPaused: false,
+    int debugPort: observatoryDefaultPort,
     Map<String, dynamic> platformArgs
   }) async {
     // TODO(chinmaygarde): Use checked, mainPath, route, clearLogs.
+    // TODO(devoncarew): Handle startPaused, debugPort.
     printTrace('Building ${app.name} for $id');
 
     // Step 1: Install the precompiled application if necessary
@@ -431,9 +435,12 @@ class IOSSimulator extends Device {
     String route,
     bool checked: true,
     bool clearLogs: false,
+    bool startPaused: false,
+    int debugPort: observatoryDefaultPort,
     Map<String, dynamic> platformArgs
   }) async {
     // TODO(chinmaygarde): Use checked, mainPath, route.
+    // TODO(devoncarew): Handle startPaused, debugPort.
     printTrace('Building ${app.name} for $id');
 
     if (clearLogs)