Do not try to use an HTML embed instead of a Flash one inside a PluginDocument.

third_party/WebKit/Source/core/html/PluginDocument.cpp

 /*
  * Copyright (C) 2006, 2008 Apple 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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 160 matching lines @@
 }
 
 DocumentParser* PluginDocument::createParser()
 {
     return PluginDocumentParser::create(this);
 }
 
 Widget* PluginDocument::pluginWidget()
 {
     if (m_pluginNode && m_pluginNode->layoutObject()) {
-        ASSERT(m_pluginNode->layoutObject()->isEmbeddedObject());
+        CHECK(m_pluginNode->layoutObject()->isEmbeddedObject());
         return toLayoutEmbeddedObject(m_pluginNode->layoutObject())->widget();
     }
     return 0;
 }
 
 Node* PluginDocument::pluginNode()
 {
     return m_pluginNode.get();
 }
 
 void PluginDocument::detachLayoutTree(const AttachContext& context)
 {
     // Release the plugin node so that we don't have a circular reference.
     m_pluginNode = nullptr;
     HTMLDocument::detachLayoutTree(context);
 }
 
 DEFINE_TRACE(PluginDocument)
 {
     visitor->trace(m_pluginNode);
     HTMLDocument::trace(visitor);
 }
 
 } // namespace blink