Fix calling convention for Chromoting's NP_Shutdown entry points

remoting/host/host_plugin.cc

Index: remoting/host/host_plugin.cc
===================================================================
--- remoting/host/host_plugin.cc	(revision 88453)
+++ remoting/host/host_plugin.cc	(working copy)
@@ -931,7 +931,7 @@
   return NPERR_NO_ERROR;
 }
 
-EXPORT NPError NP_Shutdown() {
+EXPORT NPError API_CALL NP_Shutdown() {
   LOG(INFO) << "NP_Shutdown";
   delete g_at_exit_manager;
   g_at_exit_manager = NULL;