Update PPAPI IDL generator to define versioned structs, and unversioned typedef.

ppapi/thunk/ppb_messaging_thunk.cc

Index: ppapi/thunk/ppb_messaging_thunk.cc
diff --git a/ppapi/thunk/ppb_messaging_thunk.cc b/ppapi/thunk/ppb_messaging_thunk.cc
index 8b534e0236806055dc062920778fe2b29267f15b..fe32d3e6a4ef03f847dddee201127a278b5ba97f 100644
--- a/ppapi/thunk/ppb_messaging_thunk.cc
+++ b/ppapi/thunk/ppb_messaging_thunk.cc
@@ -24,7 +24,7 @@ const PPB_Messaging g_ppb_messaging_thunk = {
 
 }  // namespace
 
-const PPB_Messaging* GetPPB_Messaging_Thunk() {
+const PPB_Messaging_1_0* GetPPB_Messaging_1_0_Thunk() {
   return &g_ppb_messaging_thunk;
 }