Add option to silence driver extension errors (#19247)

packages/flutter_driver/lib/src/extension/extension.dart

@@ -37,14 +37,15 @@ const String _extensionMethod = 'ext.flutter.$_extensionMethodName';
 typedef Future<String> DataHandler(String message);
 
 class _DriverBinding extends BindingBase with ServicesBinding, SchedulerBinding, GestureBinding, PaintingBinding, RendererBinding, WidgetsBinding {
-  _DriverBinding(this._handler);
+  _DriverBinding(this._handler, this._silenceErrors);
 
   final DataHandler _handler;
+  final bool _silenceErrors;
 
   @override
   void initServiceExtensions() {
     super.initServiceExtensions();
-    final FlutterDriverExtension extension = new FlutterDriverExtension(_handler);
+    final FlutterDriverExtension extension = new FlutterDriverExtension(_handler, _silenceErrors);
     registerServiceExtension(
       name: _extensionMethodName,
       callback: extension.call,
@@ -62,9 +63,14 @@ class _DriverBinding extends BindingBase with ServicesBinding, SchedulerBinding,
 ///
 /// Optionally you can pass a [DataHandler] callback. It will be called if the
 /// test calls [FlutterDriver.requestData].
-void enableFlutterDriverExtension({ DataHandler handler }) {
+/// 
+/// `slienceErrors` will prevent exceptions from being logged. This is useful
+/// for tests where exceptions are expected. Defaults to false. Any errors
+/// will still be returned in the `response` field of the result json along
+/// with an `isError` boolean.
+void enableFlutterDriverExtension({ DataHandler handler, bool silenceErrors = false }) {
   assert(WidgetsBinding.instance == null);
-  new _DriverBinding(handler);
+  new _DriverBinding(handler, silenceErrors);
   assert(WidgetsBinding.instance is _DriverBinding);
 }
 
@@ -88,7 +94,7 @@ class FlutterDriverExtension {
   final TestTextInput _testTextInput = new TestTextInput();
 
   /// Creates an object to manage a Flutter Driver connection.
-  FlutterDriverExtension(this._requestDataHandler) {
+  FlutterDriverExtension(this._requestDataHandler, this._silenceErrors) {
     _testTextInput.register();
 
     _commandHandlers.addAll(<String, CommandHandlerCallback>{
@@ -136,6 +142,7 @@ class FlutterDriverExtension {
   }
 
   final DataHandler _requestDataHandler;
+  final bool _silenceErrors;
 
   static final Logger _log = new Logger('FlutterDriverExtension');
 
@@ -176,7 +183,8 @@ class FlutterDriverExtension {
       return _makeResponse(msg, isError: true);
     } catch (error, stackTrace) {
       final String msg = 'Uncaught extension error while executing $commandKind: $error\n$stackTrace';
-      _log.error(msg);
+      if (!_silenceErrors)
+        _log.error(msg);
       return _makeResponse(msg, isError: true);
     }
   }

packages/flutter_driver/test/src/extension_test.dart

@@ -19,7 +19,7 @@ void main() {
 
     setUp(() {
       result = null;
-      extension = new FlutterDriverExtension((String message) async { log.add(message); return (messageId += 1).toString(); });
+      extension = new FlutterDriverExtension((String message) async { log.add(message); return (messageId += 1).toString(); }, false);
     });
 
     testWidgets('returns immediately when transient callback queue is empty', (WidgetTester tester) async {
@@ -74,7 +74,7 @@ void main() {
   group('getSemanticsId', () {
     FlutterDriverExtension extension;
     setUp(() {
-       extension = new FlutterDriverExtension((String arg) async {});
+      extension = new FlutterDriverExtension((String arg) async {}, true);
     });
 
     testWidgets('works when semantics are enabled', (WidgetTester tester) async {