Make sure to process WebSocket frames when closing a WebSocket

sdk/lib/io/websocket_impl.dart

Index: sdk/lib/io/websocket_impl.dart
diff --git a/sdk/lib/io/websocket_impl.dart b/sdk/lib/io/websocket_impl.dart
index 6e308094aabceb22ef8580c0e658a8cecdc649c4..265760690923f502512435c8e6d8df3d1fada22a 100644
--- a/sdk/lib/io/websocket_impl.dart
+++ b/sdk/lib/io/websocket_impl.dart
@@ -959,16 +959,26 @@ class _WebSocketImpl extends Stream with _ServiceObject implements WebSocket {
       _outCloseCode = code;
       _outCloseReason = reason;
     }
-    if (_closeTimer == null && !_controller.isClosed) {
-      // When closing the web-socket, we no longer accept data.
-      _closeTimer = new Timer(const Duration(seconds: 5), () {
-        // Reuse code and reason from the local close.
-        _closeCode = _outCloseCode;
-        _closeReason = _outCloseReason;
-        _subscription.cancel();
-        _controller.close();
-        _webSockets.remove(_serviceId);
-      });
+    if (!_controller.isClosed) {
+      // If a close has not yet been received from the other end then
+      //   1) make sure to listen on the stream so the close frame will be
+      //      processed if received.
+      //   2) set a timer terminate the connection if a close frame is
+      //      not received.
+      if (!_controller.hasListener) {
+        _controller.stream.drain().catchError((_) => {});
+      }
+      if (_closeTimer == null) {
+        // When closing the web-socket, we no longer accept data.
+        _closeTimer = new Timer(const Duration(seconds: 5), () {
+          // Reuse code and reason from the local close.
+          _closeCode = _outCloseCode;
+          _closeReason = _outCloseReason;
+          _subscription.cancel();
+          _controller.close();
+          _webSockets.remove(_serviceId);
+        });
+      }
     }
     return _sink.close();
   }