Add stack chain support to pkg/watcher and pkg/http.

pkg/watcher/lib/src/directory_watcher/polling.dart

Index: pkg/watcher/lib/src/directory_watcher/polling.dart
diff --git a/pkg/watcher/lib/src/directory_watcher/polling.dart b/pkg/watcher/lib/src/directory_watcher/polling.dart
index e50a0c05c148e1601088f94c074e390b9bed0454..684f7aad8ba21ef665739d0f1184ddb1281ce20f 100644
--- a/pkg/watcher/lib/src/directory_watcher/polling.dart
+++ b/pkg/watcher/lib/src/directory_watcher/polling.dart
@@ -8,6 +8,7 @@ import 'dart:async';
 import 'dart:io';
 
 import 'package:crypto/crypto.dart';
+import 'package:stack_trace/stack_trace.dart';
 
 import '../async_queue.dart';
 import '../stat.dart';
@@ -105,7 +106,7 @@ class _PollingDirectoryWatcher implements ManuallyClosedDirectoryWatcher {
       _filesToProcess.add(null);
     }
 
-    var stream = new Directory(directory).list(recursive: true);
+    var stream = Chain.track(new Directory(directory).list(recursive: true));
     _listSubscription = stream.listen((entity) {
       assert(!_events.isClosed);
 
@@ -185,7 +186,7 @@ class _PollingDirectoryWatcher implements ManuallyClosedDirectoryWatcher {
 
   /// Calculates the SHA-1 hash of the file at [path].
   Future<List<int>> _hashFile(String path) {
-    return new File(path).readAsBytes().then((bytes) {
+    return Chain.track(new File(path).readAsBytes()).then((bytes) {
       var sha1 = new SHA1();
       sha1.add(bytes);
       return sha1.close();