Fixed SetEnableRendering() in nsDocumentViewer.cpp

Initialized mEnableRendering in constructors of nsDocumentViewer.cpp and nsPlugin.cpp to a default value of PR_TRU
Do EnableRefresh only if mEnableRendering is set to true in nsHTMLContentSink.cpp,nsXMLContentSink.cpp,
nsXMLContentSink.h

modules/plugin/base/src/nsPluginViewer.cpp

@@ -186,6 +186,7 @@ PluginViewerImpl::PluginViewerImpl(const char* aCommand,
   NS_INIT_REFCNT();
   nsIStreamListener* it = new PluginListener(this);
   *aDocListener = it;
+  mEnableRendering = PR_TRUE;
 }
 
 // ISupports implementation...