Convert the PluginService interface to be an async wrapper around PluginList.

webkit/plugins/npapi/plugin_list.cc

Index: webkit/plugins/npapi/plugin_list.cc
diff --git a/webkit/plugins/npapi/plugin_list.cc b/webkit/plugins/npapi/plugin_list.cc
index a7f6dd44829629eda5c2a71fe1a9e72e6517074f..1997a4dfcf81dfcc4c74f8f6912187e4a2b19594 100644
--- a/webkit/plugins/npapi/plugin_list.cc
+++ b/webkit/plugins/npapi/plugin_list.cc
@@ -444,6 +444,10 @@ void PluginList::LoadPlugin(const FilePath& path,
 
 void PluginList::GetPlugins(std::vector<WebPluginInfo>* plugins) {
   LoadPlugins();
+  GetCachedPlugins(plugins);
+}
+
+void PluginList::GetCachedPlugins(std::vector<webkit::WebPluginInfo>* plugins) {
   base::AutoLock lock(lock_);
   for (size_t i = 0; i < plugin_groups_.size(); ++i) {
     const std::vector<webkit::WebPluginInfo>& gr_plugins =