Make sure to drain stderr in tests so that spawned process doesn't hang.

utils/tests/pub/test_pub.dart

Index: utils/tests/pub/test_pub.dart
diff --git a/utils/tests/pub/test_pub.dart b/utils/tests/pub/test_pub.dart
index ba0ba0e86202c2b299e48abb88e1e2f3bf466eb9..61afc27b73c1eb5168a717b8244615d010a5a43e 100644
--- a/utils/tests/pub/test_pub.dart
+++ b/utils/tests/pub/test_pub.dart
@@ -1268,7 +1268,7 @@ Future<Pair<List<String>, List<String>>> schedulePackageValidation(
   });
 }
 
-/// A matcher that matches a Pair.	
+/// A matcher that matches a Pair.
 Matcher pairOf(Matcher firstMatcher, Matcher lastMatcher) =>
    new _PairMatcher(firstMatcher, lastMatcher);
 
@@ -1334,8 +1334,8 @@ class ScheduledProcess {
   /// Wraps a [Process] [Future] in a scheduled process.
   ScheduledProcess(this.name, Future<Process> process)
     : _process = process,
-      _stdout = process.transform((p) => new StringInputStream(p.stdout)),
-      _stderr = process.transform((p) => new StringInputStream(p.stderr)) {
+      _stdout = process.transform((p) => _wrapStream(p.stdout)),
+      _stderr = process.transform((p) => _wrapStream(p.stderr)) {
 
     _schedule((_) {
       if (!_endScheduled) {
@@ -1466,6 +1466,12 @@ class ScheduledProcess {
     });
   }
 
+  /// Wraps [source] and ensures it gets eagerly drained. We do this to make
+  /// sure a process will exit even if we don't care about its output.
+  static Future<StringInputStream> _wrapStream(InputStream source) {
+    return new StringInputStream(wrapInputStream(source));
+  }
+
   /// Prints the remaining data in the process's stdout and stderr streams.
   /// Prints nothing if the straems are empty.
   Future _printStreams() {