Move pub/barback's Pool class into its own package.

pkg/barback/lib/src/utils/file_pool.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.
 
 library barback.utils.file_pool;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
+import 'package:pool/pool.dart';

[Bob Nystrom, 2014/07/17 22:09:14]

How about giving this a bit more specific name. Maybe "resource_pool"?

[nweiz, 2014/07/17 22:56:55]

I can if you want, but I think in a programming context it's reasonably clear
that "pool" refers to resources. It doesn't seem worthwhile to make people type
longer names when using the package if it's not disambiguating between things
they're likely to mix up.

Also I don't really like the idea of juxtaposing "ResourcePool" and
"PoolResource" classes.

[Bob Nystrom, 2014/07/21 17:47:36]

Maybe it's just my background, but I'd actually expect it to be an object or
memory pool.
Yeah, that would be weird. Just "pool" SGTM I guess.

 import 'package:stack_trace/stack_trace.dart';
 
 import '../utils.dart';
-import 'pool.dart';
 
 /// Manages a pool of files that are opened for reading to cope with maximum
 /// file descriptor limits.
 ///
 /// If a file cannot be opened because too many files are already open, this
 /// will defer the open until a previously opened file is closed and then try
 /// again. If this doesn't succeed after a certain amount of time, the open
 /// will fail and the original "too many files" exception will be thrown.
 class FilePool {
   /// The underlying pool.
@@ skipping 32 matching lines @@
     var completer = new Completer<List<int>>();
     var builder = new BytesBuilder();
 
     openRead(path).listen(builder.add, onDone: () {
       completer.complete(builder.takeBytes());
     }, onError: completer.completeError, cancelOnError: true);
 
     return completer.future;
   }
 }