Use PostTaskAndReplyWithResult in plugin_service_impl.cc.

content/test/fake_plugin_service.cc

Index: content/test/fake_plugin_service.cc
diff --git a/content/test/fake_plugin_service.cc b/content/test/fake_plugin_service.cc
index f34ac599adc77ee960d18102fd9918f01ca8648e..6746b9f16e7e86057c18920785a9a275ec2149c5 100644
--- a/content/test/fake_plugin_service.cc
+++ b/content/test/fake_plugin_service.cc
@@ -49,8 +49,7 @@ base::string16 FakePluginService::GetPluginDisplayNameByPath(
   return base::string16();
 }
 
-void FakePluginService::GetPlugins(const GetPluginsCallback& callback) {
-}
+void FakePluginService::GetPlugins(GetPluginsCallback callback) {}
 
 PepperPluginInfo* FakePluginService::GetRegisteredPpapiPluginInfo(
     const base::FilePath& plugin_path) {