Avoid WebSocket::stop() being processed twice

Source/modules/websockets/WebSocket.cpp

Index: Source/modules/websockets/WebSocket.cpp
diff --git a/Source/modules/websockets/WebSocket.cpp b/Source/modules/websockets/WebSocket.cpp
index d9521189d1f1cc283f7ed38d28e4e125ee4bd939..f91ecaad6ac33ddc73c23d5db3b5f6ca6f8cd0ca 100644
--- a/Source/modules/websockets/WebSocket.cpp
+++ b/Source/modules/websockets/WebSocket.cpp
@@ -489,14 +489,18 @@ void WebSocket::resume()
 
 void WebSocket::stop()
 {
-    bool pending = hasPendingActivity();
-    if (m_channel)
+    if (!hasPendingActivity()) {
+        ASSERT(!m_channel);
+        ASSERT(m_state == CLOSED);
+        return;
+    }
+    if (m_channel) {
         m_channel->disconnect();
-    m_channel = 0;
+        m_channel = 0;
+    }
     m_state = CLOSED;
     ActiveDOMObject::stop();
-    if (pending)
-        ActiveDOMObject::unsetPendingActivity(this);
+    ActiveDOMObject::unsetPendingActivity(this);
 }
 
 void WebSocket::didConnect()