Fix a batch of DDC SDK compile errors.

sdk/lib/io/file_impl.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.
 
 part of dart.io;
 
 // Read the file in blocks of size 64k.
 const int _BLOCK_SIZE = 64 * 1024;
 
 class _FileStream extends Stream<List<int>> {
@@ skipping 180 matching lines @@
         } catch (e, stackTrace) {
           error(e, stackTrace);
         }
       }, onDone: () {
         completer.complete(_file);
       }, onError: error, cancelOnError: true);
     }).catchError(completer.completeError);
     return completer.future;
   }
 
-  Future<File> close() =>
-      _openFuture.then<File>((openedFile) => openedFile.close());
+  Future close() => _openFuture.then((openedFile) => openedFile.close());

[floitsch, 2017/04/27 22:10:25]

Please use my changes instead:
https://codereview.chromium.org/2764943002/

[Bob Nystrom, 2017/04/28 00:13:07]

Done. (FWIW, I changed it the way I did because _FileStream is private and every
use of its close() method I saw didn't use the result value anyway.)

 }
 
 // Class for encapsulating the native implementation of files.
 class _File extends FileSystemEntity implements File {
   final String path;
 
   // Constructor for file.
   _File(this.path) {
     if (path is! String) {
       throw new ArgumentError('${Error.safeToString(path)} '
@@ skipping 335 matching lines @@
       _tryDecode(readAsBytesSync(), encoding);
 
   Future<List<String>> readAsLines({Encoding encoding: UTF8}) =>
       readAsString(encoding: encoding).then(const LineSplitter().convert);
 
   List<String> readAsLinesSync({Encoding encoding: UTF8}) =>
       const LineSplitter().convert(readAsStringSync(encoding: encoding));
 
   Future<File> writeAsBytes(List<int> bytes,
       {FileMode mode: FileMode.WRITE, bool flush: false}) {
-    return open(mode: mode).then((file) {
-      return file.writeFrom(bytes, 0, bytes.length).then((_) {
-        if (flush) return file.flush().then((_) => this);
-        return this;
-      }).whenComplete(file.close);
+    return open(mode: mode).then((file) async {

[floitsch, 2017/04/27 22:10:25]

The core libraries currently do not use 'async'. I wouldn't start here.
Especially, since there is no need.

[Bob Nystrom, 2017/04/28 00:13:07]

Took your change instead. I could have sworn I tried that same fix but it didn't
fully satisfy the type system, I think related to the body of the function
returning a Future<File> in one branch and a File in the other. Seems to be
working now. <shrug> Maybe I put the <File> on the wrong .then().

Is there a reason the core libraries don't use async? I'd expect us to want to
always dogfood the latest language features when we can.

+      try {
+        await file.writeFrom(bytes, 0, bytes.length);
+        if (flush) await file.flush();
+        return this as File;
+      } finally {
+        await file.close();
+      }
     });
   }
 
   void writeAsBytesSync(List<int> bytes,
       {FileMode mode: FileMode.WRITE, bool flush: false}) {
     RandomAccessFile opened = openSync(mode: mode);
     try {
       opened.writeFromSync(bytes, 0, bytes.length);
       if (flush) opened.flushSync();
     } finally {
@@ skipping 491 matching lines @@
   void _checkAvailable() {
     if (_asyncDispatched) {
       throw new FileSystemException(
           "An async operation is currently pending", path);
     }
     if (closed) {
       throw new FileSystemException("File closed", path);
     }
   }
 }