Added an assertion verifying that a Canvas2DLayerBridge is not deleted

Source/platform/graphics/Canvas2DLayerBridge.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 98 matching lines @@
     m_layer->setRateLimitContext(m_rateLimitingEnabled);
     m_canvas->setNotificationClient(this);
 #ifndef NDEBUG
     canvas2DLayerBridgeInstanceCounter.increment();
 #endif
 }
 
 Canvas2DLayerBridge::~Canvas2DLayerBridge()
 {
     ASSERT(m_destructionInProgress);
+    ASSERT(!Canvas2DLayerManager::get().isInList(this));
     m_layer.clear();
     freeReleasedMailbox();
 #if ASSERT_ENABLED
     Vector<MailboxInfo>::iterator mailboxInfo;
     for (mailboxInfo = m_mailboxes.begin(); mailboxInfo < m_mailboxes.end(); ++mailboxInfo) {
         ASSERT(mailboxInfo->m_status != MailboxInUse);
         ASSERT(mailboxInfo->m_status != MailboxReleased || m_contextProvider->context3d()->isContextLost() || !m_isSurfaceValid);
     }
 #endif
     m_mailboxes.clear();
@@ skipping 404 matching lines @@
 Canvas2DLayerBridge::MailboxInfo::MailboxInfo(const MailboxInfo& other) {
     // This copy constructor should only be used for Vector reallocation
     // Assuming 'other' is to be destroyed, we transfer m_image ownership
     // rather than do a refcount dance.
     memcpy(&m_mailbox, &other.m_mailbox, sizeof(m_mailbox));
     m_image = const_cast<MailboxInfo*>(&other)->m_image.release();
     m_status = other.m_status;
 }
 
 }