Add a --pause-after-load flag for debugging.

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 fb2632f62c43f5eae3ac525dc01714fe31b4f8d9..cb4e6285f08852add9d4d640eb07f0b3399394a3 100644
--- a/lib/src/util/io.dart
+++ b/lib/src/util/io.dart
@@ -5,14 +5,17 @@
 library test.util.io;
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
 import 'dart:mirrors';
 
+import 'package:async/async.dart';
 import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 
 import '../backend/operating_system.dart';
 import '../runner/application_exception.dart';
+import '../utils.dart';
 
 /// The ASCII code for a newline character.
 const _newline = 0xA;
@@ -46,6 +49,10 @@ final OperatingSystem currentOS = (() {
   throw new UnsupportedError('Unsupported operating system "$name".');
 })();
 
+/// A queue of lines of standard input.
+final stdinLines = new StreamQueue(
+    UTF8.decoder.fuse(const LineSplitter()).bind(stdin));
+
 /// The root directory below which to nest temporary directories created by the
 /// test runner.
 ///
@@ -131,6 +138,19 @@ Stream<List<int>> sanitizeForWindows(Stream<List<int>> input) {
   });
 }
 
+/// Print a warning containing [message].
+///
+/// This automatically wraps lines if they get too long. If [color] is passed,
+/// it controls whether the warning header is color; otherwise, it defaults to
+/// [canUseSpecialChars].
+void warn(String message, {bool color}) {
+  if (color == null) color = canUseSpecialChars;
+  var header = color
+      ? "\u001b[33mWarning:\u001b[0m"
+      : "Warning:";
+  stderr.writeln(wordWrap("$header $message\n"));
+}
+
 /// Creates a URL string for [address]:[port].
 ///
 /// Handles properly formatting IPv6 addresses.