Add support for --pub-serve.

test/io.dart

Index: test/io.dart
diff --git a/test/io.dart b/test/io.dart
index 9dccdaef5772d4ed5f3c1430ca33f7ea67b2d504..dcfe3b910817198f547991c618d8607149161f62 100644
--- a/test/io.dart
+++ b/test/io.dart
@@ -4,6 +4,7 @@
 
 library test.test.io;
 
+import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ -12,6 +13,11 @@ import 'package:test/src/util/io.dart';
 /// The path to the root directory of the `test` package.
 final String packageDir = p.dirname(p.dirname(libraryPath(#test.test.io)));
 
+/// The path to the `pub` executable in the current Dart SDK.
+final _pubPath = p.join(
+    p.dirname(Platform.executable),
+    Platform.isWindows ? 'pub.bat' : 'pub');
+
 /// Runs the test executable with the package root set properly.
 ProcessResult runUnittest(List<String> args, {String workingDirectory,
     Map<String, String> environment}) {
@@ -37,3 +43,19 @@ ProcessResult runDart(List<String> args, {String workingDirectory,
   return Process.runSync(Platform.executable, allArgs,
       workingDirectory: workingDirectory, environment: environment);
 }
+
+/// Runs Pub.
+ProcessResult runPub(List<String> args, {String workingDirectory,
+    Map<String, String> environment}) {
+  // TODO(nweiz): Use ScheduledProcess once it's compatible.
+  return Process.runSync(_pubPath, args,
+      workingDirectory: workingDirectory, environment: environment);
+}
+
+/// Starts Pub.
+Future<Process> startPub(List<String> args, {String workingDirectory,
+    Map<String, String> environment}) {
+  // TODO(nweiz): Use ScheduledProcess once it's compatible.
+  return Process.start(_pubPath, args,
+      workingDirectory: workingDirectory, environment: environment);
+}