Fix crash in raw_secure_server_socket_test.

runtime/bin/socket_patch.dart

Index: runtime/bin/socket_patch.dart
diff --git a/runtime/bin/socket_patch.dart b/runtime/bin/socket_patch.dart
index 030a9058cc9409517c0b116b94c071a970be7813..98de2a0bea00ed304ad9d19ff9fdcdbe506d2bae 100644
--- a/runtime/bin/socket_patch.dart
+++ b/runtime/bin/socket_patch.dart
@@ -824,6 +824,7 @@ class _NativeSocket extends NativeFieldWrapperClass1 {
 
         var handler = eventHandlers[i];
         if (i == DESTROYED_EVENT) {
+          assert(isClosing);
           assert(!isClosed);
           isClosed = true;
           closeCompleter.complete();
@@ -873,7 +874,7 @@ class _NativeSocket extends NativeFieldWrapperClass1 {
     sendWriteEvents = write;
     if (read) issueReadEvent();
     if (write) issueWriteEvent();
-    if (eventPort == null) {
+    if (eventPort == null && !isClosing) {
       int flags = typeFlags & TYPE_TYPE_MASK;
       if (!isClosedRead) flags |= 1 << READ_EVENT;
       if (!isClosedWrite) flags |= 1 << WRITE_EVENT;
@@ -936,6 +937,7 @@ class _NativeSocket extends NativeFieldWrapperClass1 {
   }
 
   void connectToEventHandler() {
+    assert(!isClosed);
     if (eventPort == null) {
       eventPort = new RawReceivePort(multiplex);
       _SocketsObservatory.add(this);