Make sure resource client is called asynchronously

Source/core/fetch/Resource.cpp

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller (mueller@kde.org)
     Copyright (C) 2002 Waldo Bastian (bastian@kde.org)
     Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
@@ skipping 545 matching lines @@
 }
 
 void Resource::didAccessDecodedData()
 {
     memoryCache()->updateDecodedResource(this, UpdateForAccess);
     memoryCache()->prune();
 }
 
 void Resource::finishPendingClients()
 {
-    while (!m_clientsAwaitingCallback.isEmpty()) {
-        ResourceClient* client = m_clientsAwaitingCallback.begin()->key;
-        m_clientsAwaitingCallback.remove(client);
-        m_clients.add(client);
-        didAddClient(client);
+    // Clients can be added during the loop. We must not process them now.
+    // So save the current set to the stack.
+    HashCountedSet<ResourceClient*> clientsAwaitingCallback;
+    clientsAwaitingCallback.swap(m_clientsAwaitingCallback);
+
+    for (HashCountedSet<ResourceClient*>::iterator it = clientsAwaitingCallback.begin(); it != clientsAwaitingCallback.end(); ++it) {
+        m_clients.add(it->key);
+        didAddClient(it->key);
     }
+    // It is a critical problem if a callback is scheduled but there is no client waiting for it.
+    // Such a callback cannot be cancelled. It is better to crash the renderer now.
+    RELEASE_ASSERT(!ResourceCallback::callbackHandler()->isScheduled(this) || !m_clientsAwaitingCallback.isEmpty());
 }
 
 void Resource::prune()
 {
     destroyDecodedDataIfPossible();
     unlock();
 }
 
 void Resource::setResourceToRevalidate(Resource* resource)
 {
@@ skipping 360 matching lines @@
         return "Shader";
     case Resource::ImportResource:
         return "ImportResource";
     }
     ASSERT_NOT_REACHED();
     return "Unknown";
 }
 #endif // !LOG_DISABLED
 
 }