Make new StreamController be async by default.

pkg/logging/lib/logging.dart

Index: pkg/logging/lib/logging.dart
diff --git a/pkg/logging/lib/logging.dart b/pkg/logging/lib/logging.dart
index 94bf5f3dfdc3d51412980b4561a347f552097a02..b29f076cb0a225c604c2fd61f32bca07b61c9d5b 100644
--- a/pkg/logging/lib/logging.dart
+++ b/pkg/logging/lib/logging.dart
@@ -196,7 +196,7 @@ class Logger {
   Stream<LogRecord> _getStream() {
     if (hierarchicalLoggingEnabled || parent == null) {
       if (_controller == null) {
-        _controller = new StreamController<LogRecord>();
+        _controller = new StreamController<LogRecord>(sync: true);
         _stream = _controller.stream.asBroadcastStream();
       }
       return _stream;