Add a CompilerPool class.

lib/src/util/io.dart

 // Copyright (c) 2015, 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 unittest.util.io;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 
+/// The root directory of the Dart SDK.
+final String sdkDir = _computeSdkDir();
+String _computeSdkDir() => p.dirname(p.dirname(Platform.executable));
+
 /// Returns whether the current Dart version supports [Isolate.kill].
 final bool supportsIsolateKill = _supportsIsolateKill;
 bool get _supportsIsolateKill {
   // This isn't 100% accurate, since early 1.9 dev releases didn't support
   // Isolate.kill(), but it's very unlikely anyone will be using them.
   // TODO(nweiz): remove this when we no longer support older Dart versions.
   var path = p.join(p.dirname(p.dirname(Platform.executable)), 'version');
   return new File(path).readAsStringSync().startsWith('1.9');
 }
 
@@ skipping 24 matching lines @@
 /// [fn] completes to.
 Future withTempDir(Future fn(String path)) {
   return new Future.sync(() {
     // TODO(nweiz): Empirically test whether sync or async functions perform
     // better here when starting a bunch of isolates.
     var tempDir = Directory.systemTemp.createTempSync('unittest_');
     return new Future.sync(() => fn(tempDir.path))
         .whenComplete(() => tempDir.deleteSync(recursive: true));
   });
 }