Missing handling of default arguments in socket stream readInto

runtime/bin/socket_stream_impl.dart

Index: runtime/bin/socket_stream_impl.dart
diff --git a/runtime/bin/socket_stream_impl.dart b/runtime/bin/socket_stream_impl.dart
index 3c3dfade321d25e93eae23a50c5bb24d2668c86f..819a1a6495183b6494dd631f179f5ee4967f6a86 100644
--- a/runtime/bin/socket_stream_impl.dart
+++ b/runtime/bin/socket_stream_impl.dart
@@ -35,8 +35,8 @@ class _SocketInputStream implements SocketInputStream {
     }
   }
 
-  int readInto(List<int> buffer, int offset, int len) {
-    if (offset === null) offset = 0;
+  int readInto(List<int> buffer, [int offset = 0, int len]) {
+    if (_closed) return null;
     if (len === null) len = buffer.length;
     if (offset < 0) throw new StreamException("Illegal offset $offset");
     if (len < 0) throw new StreamException("Illegal length $len");