Pass method used to start flutter application (#27812)

packages/flutter_tools/doc/daemon.md

@@ -109,7 +109,7 @@ The `stop()` command takes one parameter, `appId`. It returns a `bool` to indica
 
 #### app.start
 
-This is sent when an app is starting. The `params` field will be a map with the fields `appId`, `directory`, and `deviceId`.
+This is sent when an app is starting. The `params` field will be a map with the fields `appId`, `directory`, `deviceId`, and `launchMode`.
 
 #### app.debugPort
 

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

@@ -221,6 +221,7 @@ class AttachCommand extends FlutterCommand {
             null,
             true,
             fs.currentDirectory,
+            LaunchMode.attach,
           );
         } catch (error) {
           throwToolExit(error.toString());

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

@@ -400,6 +400,7 @@ class AppDomain extends Domain {
       projectDirectory,
       enableHotReload,
       cwd,
+      LaunchMode.run,
     );
   }
 
@@ -409,7 +410,8 @@ class AppDomain extends Domain {
       Device device,
       String projectDirectory,
       bool enableHotReload,
-      Directory cwd) async {
+      Directory cwd,
+      LaunchMode launchMode) async {
     final AppInstance app = AppInstance(_getNewAppId(),
         runner: runner, logToStdout: daemon.logToStdout);
     _apps.add(app);
@@ -417,6 +419,7 @@ class AppDomain extends Domain {
       'deviceId': device.id,
       'directory': projectDirectory,
       'supportsRestart': isRestartSupported(enableHotReload, device),
+      'launchMode': launchMode.toString(),
     });
 
     Completer<DebugConnectionInfo> connectionInfoCompleter;
@@ -1021,3 +1024,19 @@ class LogMessage {
   final String message;
   final StackTrace stackTrace;
 }
+
+/// The method by which the flutter app was launched.
+class LaunchMode {
+  const LaunchMode._(this._value);
+
+  /// The app was launched via `flutter run`.
+  static const LaunchMode run = LaunchMode._('run');
+
+  /// The app was launched via `flutter attach`.
+  static const LaunchMode attach = LaunchMode._('attach');
+
+  final String _value;
+
+  @override
+  String toString() => _value;
+}

packages/flutter_tools/tool/daemon_client.dart

@@ -42,7 +42,8 @@ Future<void> main() async {
         'method': 'app.start',
         'params': <String, dynamic> {
           'deviceId': words[1],
-          'projectDirectory': words[2]
+          'projectDirectory': words[2],
+          'launchMode': words[3],
         }
       });
     } else if (words.first == 'stop') {