better error message when WebDriver/Selenium not available #50146
Description
From crash logging for the flutter drive -d chrome command on master/1.14.7-pre.101 First seen in master/1.14.7-pre.27.
SocketException: Connection failed (OS Error: No connection could be made because the target machine actively refused it., errno = 10061), address = localhost, port = 4444
| at _NativeSynchronousSocket.connectSync.connectNext | (sync_socket_patch.dart:91 )
| at _NativeSynchronousSocket.connectSync.connectNext | (sync_socket_patch.dart:102 )
| at _NativeSynchronousSocket.connectSync.connectNext | (sync_socket_patch.dart:102 )
| at _NativeSynchronousSocket.connectSync | (sync_socket_patch.dart:118 )
| at _RawSynchronousSocket.connectSync | (sync_socket_patch.dart:25 )
| at RawSynchronousSocket.connectSync | (sync_socket_patch.dart:13 )
| at new SyncHttpClientRequest._ | (sync_http.dart:67 )
| at SyncHttpClient.postUrl | (sync_http.dart:20 )
| at SyncHttpRequestClient.sendRaw | (sync_http_request_client.dart:20 )
| at SyncRequestClient.send | (request_client.dart:46 )
| at createDriver | (sync_core.dart:63 )
| at createDriver | (sync_io.dart:35 )
| at _createDriver | (drive.dart:441 )
| at DriveCommand.runCommand | (drive.dart:182 )
| at <asynchronous gap> | (async )
| at FlutterCommand.verifyThenRunCommand | (flutter_command.dart:639 )
| at <asynchronous gap> | (async )
| at FlutterCommand.run.<anonymous closure> | (flutter_command.dart:537 )
| at <asynchronous gap> | (async )
| at AppContext.run.<anonymous closure> | (context.dart:150 )
| at _rootRun | (zone.dart:1126 )
| at _CustomZone.run | (zone.dart:1023 )
| at _runZoned | (zone.dart:1518 )
| at runZoned | (zone.dart:1465 )
| at AppContext.run | (context.dart:149 )
| at FlutterCommand.run | (flutter_command.dart:527 )
| at CommandRunner.runCommand | (command_runner.dart:197 )
| at FlutterCommandRunner.runCommand.<anonymous closure> | (flutter_command_runner.dart:338 )
| at <asynchronous gap> | (async )
| at AppContext.run.<anonymous closure> | (context.dart:150 )
| at _rootRun | (zone.dart:1126 )
| at _CustomZone.run | (zone.dart:1023 )
| at _runZoned | (zone.dart:1518 )
| at runZoned | (zone.dart:1465 )
| at AppContext.run | (context.dart:149 )
| at FlutterCommandRunner.runCommand | (flutter_command_runner.dart:288 )
| at CommandRunner.run.<anonymous closure> | (command_runner.dart:112 )
| at new Future.sync | (future.dart:224 )
| at CommandRunner.run | (command_runner.dart:112 )
| at FlutterCommandRunner.run | (flutter_command_runner.dart:231 )
| at run.<anonymous closure>.<anonymous closure> | (runner.dart:64 )
| at _rootRun | (zone.dart:1126 )
| at _CustomZone.run | (zone.dart:1023 )
| at _runZoned | (zone.dart:1518 )
| at runZoned | (zone.dart:1502 )
| at run.<anonymous closure> | (runner.dart:62 )
| at <asynchronous gap> | (async )
| at AppContext.run.<anonymous closure> | (context.dart:150 )
| at _rootRun | (zone.dart:1126 )
| at _CustomZone.run | (zone.dart:1023 )
| at _runZoned | (zone.dart:1518 )
| at runZoned | (zone.dart:1465 )
| at AppContext.run | (context.dart:149 )
| at runInContext | (context_runner.dart:64 )
| at run | (runner.dart:51 )
| at main | (executable.dart:65 )
| at main | (flutter_tools.dart:8 )
| at _startIsolate.<anonymous closure> | (isolate_patch.dart:299 )
| at _RawReceivePortImpl._handleMessage | (isolate_patch.dart:168 )