Break path whereby AssociatedURLLoader::~AssociatedURLLoader() is re-entered on top of itself.

BUG=159429

Review URL: https://chromiumcodereview.appspot.com/11359222

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@168150 0039d316-1c4b-4281-b951-d872f2087c98
WebFrame* GetFrameForResource(const Resource* resource) {
  PluginInstance* plugin_instance = ResourceHelper::GetPluginInstance(resource);
  if (!plugin_instance)
    return NULL;
  return plugin_instance->container()->element().document().frame();
}

WebFrame* GetFrameForResource(const Resource* resource) {
  PluginInstance* plugin_instance = ResourceHelper::GetPluginInstance(resource);
  if (!plugin_instance)
    return NULL;
  return plugin_instance->container()->element().document().frame();
}
