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

ppapi/thunk/ppb_buffer_thunk.cc

Index: ppapi/thunk/ppb_buffer_thunk.cc
diff --git a/ppapi/thunk/ppb_buffer_thunk.cc b/ppapi/thunk/ppb_buffer_thunk.cc
index 1772048c76a9f5b5a43b6b2d762bee4ba33ceb21..52a00ca4bd55450c579c2971aad7de32e43ec5cf 100644
--- a/ppapi/thunk/ppb_buffer_thunk.cc
+++ b/ppapi/thunk/ppb_buffer_thunk.cc
@@ -57,7 +57,7 @@ const PPB_Buffer_Dev g_ppb_buffer_thunk = {
 
 }  // namespace
 
-const PPB_Buffer_Dev* GetPPB_Buffer_Dev_Thunk() {
+const PPB_Buffer_Dev_0_4* GetPPB_Buffer_Dev_0_4_Thunk() {
   return &g_ppb_buffer_thunk;
 }