Stop working around issue 8512.

utils/pub/error_group.dart

Index: utils/pub/error_group.dart
diff --git a/utils/pub/error_group.dart b/utils/pub/error_group.dart
index dc0ba8a7fce1ef46e5212b5eb8051c80d58c1775..5e6baf859f51da72e6fbd29cb3a6cc02441fc689 100644
--- a/utils/pub/error_group.dart
+++ b/utils/pub/error_group.dart
@@ -232,10 +232,6 @@ class _ErrorGroupStream extends Stream {
   /// Whether [this] has any listeners.
   bool get _hasListeners => _controller.hasSubscribers;
 
-  // TODO(nweiz): Remove this when issue 8512 is fixed.
-  /// Whether the subscription has been cancelled.
-  bool _cancelled = false;
-
   /// Creates a new [_ErrorGroupFuture] that's a child of [_group] and wraps
   /// [inner].
   _ErrorGroupStream(this._group, Stream inner)
@@ -243,15 +239,13 @@ class _ErrorGroupStream extends Stream {
           new StreamController.broadcast() :
           new StreamController() {
     _subscription = inner.listen((v) {
-      if (!_cancelled) _controller.add(v);
+      _controller.add(v);
     }, onError: (e) {
-      if (!_cancelled) _group._signalError(e);
+      _group._signalError(e);
     }, onDone: () {
-      if (!_cancelled) {
-        _isDone = true;
-        _group._signalStreamComplete(this);
-        _controller.close();
-      }
+      _isDone = true;
+      _group._signalStreamComplete(this);
+      _controller.close();
     });
   }
 
@@ -268,7 +262,6 @@ class _ErrorGroupStream extends Stream {
   /// unless it's already complete.
   void _signalError(AsyncError e) {
     if (_isDone) return;
-    _cancelled = true;
     _subscription.cancel();
     // Call these asynchronously to work around issue 7913.
     defer(() {