Make sure all isolates start during flutter driver tests. (#65703)

packages/flutter_driver/lib/src/driver/vmservice_driver.dart

@@ -131,8 +131,22 @@ class VMServiceFlutterDriver extends FlutterDriver {
     // Attempts to resume the isolate, but does not crash if it fails because
     // the isolate is already resumed. There could be a race with other tools,
     // such as a debugger, any of which could have resumed the isolate.
-    Future<dynamic> resumeLeniently() {
+    Future<dynamic> resumeLeniently() async {
       _log('Attempting to resume isolate');
+      // Let subsequent isolates start automatically.
+      try {
+        final Map<String, dynamic> result =
+            await connection.peer.sendRequest('setFlag', <String, String>{
+          'name': 'pause_isolates_on_start',
+          'value': 'false',
+        }) as Map<String, dynamic>;
+        if (result == null || result['type'] != 'Success') {
+          _log('setFlag failure: $result');
+        }
+      } catch (e) {
+        _log('Failed to set pause_isolates_on_start=false, proceeding. Error: $e');
+      }
+
       return isolate.resume().catchError((dynamic e) {
         const int vmMustBePausedCode = 101;
         if (e is rpc.RpcException && e.code == vmMustBePausedCode) {

packages/flutter_driver/test/flutter_driver_test.dart

@@ -72,6 +72,10 @@ void main() {
         connectionLog.add('streamListen');
         return null;
       });
+      when(mockPeer.sendRequest('setFlag', any)).thenAnswer((Invocation invocation) {
+        connectionLog.add('setFlag');
+        return null;
+      });
       when(mockIsolate.pauseEvent).thenReturn(MockVMPauseStartEvent());
       when(mockIsolate.resume()).thenAnswer((Invocation invocation) {
         connectionLog.add('resume');
@@ -85,9 +89,26 @@ void main() {
       final FlutterDriver driver = await FlutterDriver.connect(dartVmServiceUrl: '');
       expect(driver, isNotNull);
       expectLogContains('Isolate is paused at start');
-      expect(connectionLog, <String>['resume', 'streamListen', 'onExtensionAdded']);
+      expect(connectionLog, <String>['setFlag', 'resume', 'streamListen', 'onExtensionAdded']);
     });
 
+    test('ignores setFlag failure', () async {
+      when(mockPeer.sendRequest('setFlag', any)).thenThrow(Exception('setFlag failed'));
+      when(mockIsolate.pauseEvent).thenReturn(MockVMPauseStartEvent());
+      when(mockIsolate.resume()).thenAnswer((Invocation invocation) {
+        return Future<dynamic>.value(null);
+      });
+      when(mockIsolate.onExtensionAdded).thenAnswer((Invocation invocation) {
+        return Stream<String>.fromIterable(<String>['ext.flutter.driver']);
+      });
+
+      final FlutterDriver driver = await FlutterDriver.connect(dartVmServiceUrl: '');
+      expectLogContains('Failed to set pause_isolates_on_start=false, proceeding. '
+                        'Error: Exception: setFlag failed');
+      expect(driver, isNotNull);
+    });
+
+
     test('connects to isolate paused mid-flight', () async {
       when(mockIsolate.pauseEvent).thenReturn(MockVMPauseBreakpointEvent());
       when(mockIsolate.resume()).thenAnswer((Invocation invocation) => Future<dynamic>.value(null));