Improve WebDriver error message (#81107)

* Add link to documentation in error message

The current WebDriver message is incomplete. Add link to
the documentation on WebDrivers for different browsers
to help troubleshooting.

packages/flutter_tools/lib/src/drive/web_driver_service.dart

@@ -109,9 +109,11 @@ class WebDriverService extends DriverService {
       );
     } on Exception catch (ex) {
       throwToolExit(
-        'Unable to start WebDriver Session for Flutter for Web testing. \n'
-        'Make sure you have the correct WebDriver Server running at $driverPort. \n'
-        'Make sure the WebDriver Server matches option --browser-name. \n'
+        'Unable to start WebDriver Session for Flutter for Web testing.\n'
+        'Make sure you have the correct WebDriver Server running at $driverPort.\n'
+        'Make sure the WebDriver Server matches option --browser-name.\n'
+        'For more information see: '
+        'https://flutter.dev/docs/testing/integration-tests#running-in-a-browser\n'
         '$ex'
       );
     }

packages/flutter_tools/test/general.shard/drive/drive_service_test.dart

@@ -16,6 +16,7 @@ import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/convert.dart';
 import 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/drive/drive_service.dart';
+import 'package:flutter_tools/src/drive/web_driver_service.dart';
 import 'package:flutter_tools/src/resident_runner.dart';
 import 'package:flutter_tools/src/version.dart';
 import 'package:flutter_tools/src/vmservice.dart';
@@ -454,6 +455,25 @@ void main() {
     );
     await driverService.stop();
   });
+
+  testWithoutContext('WebDriver error message includes link to documentation', () async {
+    const String link = 'https://flutter.dev/docs/testing/integration-tests#running-in-a-browser';
+    final DriverService driverService = WebDriverService(
+      dartSdkPath: 'dart',
+      processUtils: ProcessUtils(
+        processManager: FakeProcessManager.empty(),
+        logger: BufferLogger.test(),
+      ),
+    );
+
+    expect(() => driverService.startTest(
+      'foo.test',
+      <String>[],
+      <String, String>{},
+      PackageConfig(<Package>[Package('test', Uri.base)]),
+      browserName: 'chrome',
+    ), throwsToolExit(message: RegExp('\nFor more information see: $link\n')));
+  });
 }
 
 FlutterDriverService setUpDriverService({
@@ -517,6 +537,8 @@ class FakeDevice extends Fake implements Device {
   bool didUninstallApp = false;
   bool didDispose = false;
   bool failOnce = false;
+  @override
+  final PlatformType platformType = PlatformType.web;
 
   @override
   String get name => 'test';