added gpr_types.h
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index 02ad508..67a0803 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -847,6 +847,7 @@
include/grpc/impl/codegen/atm_gcc_atomic.h \
include/grpc/impl/codegen/atm_gcc_sync.h \
include/grpc/impl/codegen/atm_windows.h \
+include/grpc/impl/codegen/gpr_types.h \
include/grpc/impl/codegen/port_platform.h \
include/grpc/impl/codegen/slice.h \
include/grpc/impl/codegen/sync.h \