PPAPI/NaCl: Move plugin_main.cc's contents into irt_ppapi.cc

ppapi/nacl_irt/irt_ppapi.h

Index: ppapi/nacl_irt/irt_ppapi.h
diff --git a/ppapi/nacl_irt/irt_ppapi.h b/ppapi/nacl_irt/irt_ppapi.h
index d65bede29486b31dabf36b43a2d030e6b9819bc7..07a5a864065327405f5f34797f4c029bbac8866f 100644
--- a/ppapi/nacl_irt/irt_ppapi.h
+++ b/ppapi/nacl_irt/irt_ppapi.h
@@ -5,6 +5,19 @@
 #ifndef PPAPI_NACL_IRT_IRT_PPAPI_H_
 #define PPAPI_NACL_IRT_IRT_PPAPI_H_
 
-extern "C" int irt_ppapi_start(const struct PP_StartFunctions* funcs);
+#include "ppapi/nacl_irt/public/irt_ppapi.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int irt_ppapi_start(const struct PP_StartFunctions* funcs);
+
+void PpapiPluginRegisterThreadCreator(
+    const struct PP_ThreadFunctions* new_funcs);
+
+#ifdef __cplusplus
+}
+#endif
 
 #endif  // PPAPI_NACL_IRT_IRT_PPAPI_H_