Clean up dart:io warnings/errors found by analyzer tests.

tests/standalone/io/file_fuzz_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // 'fuzz' test the file APIs by providing unexpected type arguments. The test
 // passes if the VM does not crash.
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
 import 'fuzz_support.dart';
 
 fuzzSyncMethods() {
   typeMapping.forEach((k, v) {
     doItSync(() {
       var f = new File(v);
       doItSync(f.existsSync);
       doItSync(f.createSync);
       doItSync(f.deleteSync);
       doItSync(f.lengthSync);
       doItSync(f.modifiedSync);
       doItSync(f.fullPathSync);
-      doItSync(() => f.openRead().listen(() {}, onError: (e) {}));
+      doItSync(() => f.openRead().listen((_) {}, onError: (e) {}));
       doItSync(f.readAsBytesSync);
       doItSync(f.readAsStringSync);
       doItSync(f.readAsLinesSync);
       typeMapping.forEach((k2, v2) {
         doItSync(() => f.openSync(mode: v2));
         doItSync(() => f.openWrite(mode: v2));
-        doItSync(() => f.readAsStringSync(v2));
-        doItSync(() => f.readAsLinesSync(v2));
+        doItSync(() => f.readAsStringSync(encoding: v2));
+        doItSync(() => f.readAsLinesSync(encoding: v2));
       });
     });
   });
 }
 
 fuzzAsyncMethods() {
   var port = new ReceivePort();
   var futures = [];
   typeMapping.forEach((k, v) {
     doItSync(() {
       var f = new File(v);
       futures.add(doItAsync(f.exists));
       futures.add(doItAsync(f.delete));
       futures.add(doItAsync(f.directory));
       futures.add(doItAsync(f.length));
       futures.add(doItAsync(f.modified));
       futures.add(doItAsync(f.open));
       futures.add(doItAsync(f.fullPath));
       futures.add(doItAsync(f.readAsBytes));
       futures.add(doItAsync(f.readAsLines));
       futures.add(doItAsync(f.readAsString));
       typeMapping.forEach((k2, v2) {
-        futures.add(doItAsync(() => f.open(v2)));
-        futures.add(doItAsync(() => f.readAsString(v2)));
-        futures.add(doItAsync(() => f.readAsLines(v2)));
+        futures.add(doItAsync(() => f.open(mode: v2)));
+        futures.add(doItAsync(() => f.readAsString(encoding: v2)));
+        futures.add(doItAsync(() => f.readAsLines(encoding: v2)));
       });
     });
   });
   Future.wait(futures).then((ignore) => port.close());
 }
 
 
 fuzzSyncRandomAccessMethods() {
   var d = new Directory('');
   var temp = d.createTempSync();
   var file = new File('${temp.path}/x');
   file.createSync();
   var modes = [ FileMode.READ, FileMode.WRITE, FileMode.APPEND ];
   for (var m in modes) {
     var opened = file.openSync(mode: m);
     typeMapping.forEach((k, v) {
       doItSync(() => opened.setPositionSync(v));
       doItSync(() => opened.truncateSync(v));
       doItSync(() => opened.writeByteSync(v));
     });
     for (var p in typePermutations(2)) {
-      doItSync(() => opened.writeStringSync(p[0], p[1]));
+      doItSync(() => opened.writeStringSync(p[0], encoding: p[1]));
     }
     for (var p in typePermutations(3)) {
       doItSync(() => opened.readIntoSync(p[0], p[1], p[2]));
       doItSync(() => opened.writeFromSync(p[0], p[1], p[2]));
     }
     opened.closeSync();
   }
   temp.deleteSync(recursive: true);
 }
 
 fuzzAsyncRandomAccessMethods() {
   var d = new Directory('');
   var temp = d.createTempSync();
   var file = new File('${temp.path}/x');
   file.createSync();
   var modes = [ FileMode.READ, FileMode.WRITE, FileMode.APPEND ];
   var futures = [];
   var openedFiles = [];
   for (var m in modes) {
     var opened = file.openSync(mode: m);
     openedFiles.add(opened);
     typeMapping.forEach((k, v) {
         futures.add(doItAsync(() => opened.setPosition(v)));
         futures.add(doItAsync(() => opened.truncate(v)));
         futures.add(doItAsync(() => opened.writeByte(v)));
     });
     for (var p in typePermutations(2)) {
-      futures.add(doItAsync(() => opened.writeString(p[0], p[1])));
+      futures.add(doItAsync(() => opened.writeString(p[0], encoding: p[1])));
     }
     for (var p in typePermutations(3)) {
       futures.add(doItAsync(() => opened.readInto(p[0], p[1], p[2])));
       futures.add(doItAsync(() => opened.writeFrom(p[0], p[1], p[2])));
     }
   }
   Future.wait(futures).then((ignore) {
     for (var opened in openedFiles) {
       opened.closeSync();
     }
     temp.deleteSync(recursive: true);
   });
 }
 
 main() {
   fuzzSyncMethods();
   fuzzAsyncMethods();
   fuzzSyncRandomAccessMethods();
   fuzzAsyncRandomAccessMethods();
 }