Add support for --pub-serve.

lib/src/util/io.dart

Index: lib/src/util/io.dart
diff --git a/lib/src/util/io.dart b/lib/src/util/io.dart
index 39c336ac84ddff329fcecdc6fee2f9932b7110f5..047e7557c1369a7a58fd5344c3be66091ff49aca 100644
--- a/lib/src/util/io.dart
+++ b/lib/src/util/io.dart
@@ -9,6 +9,7 @@ import 'dart:io';
 import 'dart:mirrors';
 
 import 'package:path/path.dart' as p;
+import 'package:pub_semver/pub_semver.dart';
 
 import '../backend/operating_system.dart';
 import '../runner/load_exception.dart';
@@ -17,6 +18,11 @@ import '../runner/load_exception.dart';
 final String sdkDir =
     p.dirname(p.dirname(Platform.executable));
 
+/// The version of the Dart SDK currently in use.

[kevmoo, 2015/04/03 22:55:53]

Annoying nit: if this check fails, an exception will thrown the first time – and
null will be returned every time after

If the check is catastrophic to the runner, that's fine. If not, we could end up
with weird NPE errors mixed in with one stack trace with something that could
actually be debugged

+final Version _sdkVersion = new Version.parse(
+    new File(p.join(p.dirname(p.dirname(Platform.executable)), 'version'))
+        .readAsStringSync().trim());
+
 /// Returns the current operating system.
 final OperatingSystem currentOS = (() {
   var name = Platform.operatingSystem;
@@ -38,8 +44,16 @@ 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('1.8');
+  return new VersionConstraint.parse('>=1.9.0-dev <2.0.0').allows(_sdkVersion);
+}
+
+/// Returns whether the current Dart version has a fix for issue 23084.
+final bool supportsPubServe = _supportsPubServe;
+bool get _supportsPubServe {
+  // This isn't 100% accurate, since issue 23084 wasn't fixed in early 1.10 dev
+  // releases, but it's unlikely anyone will be using them.
+  // TODO(nweiz): remove this when we no longer support older Dart versions.
+  return new VersionConstraint.parse('>=1.9.2 <2.0.0').allows(_sdkVersion);
 }
 
 // TODO(nweiz): Make this check [stdioType] once that works within "pub run".