Fix sanity: check_sources_and_headers
diff --git a/tools/doxygen/Doxyfile.c++ b/tools/doxygen/Doxyfile.c++
index fa9b705..e4c0d6a 100644
--- a/tools/doxygen/Doxyfile.c++
+++ b/tools/doxygen/Doxyfile.c++
@@ -821,6 +821,7 @@
 include/grpc++/impl/codegen/server_context.h \
 include/grpc++/impl/codegen/server_interface.h \
 include/grpc++/impl/codegen/service_type.h \
+include/grpc++/impl/codegen/slice.h \
 include/grpc++/impl/codegen/status.h \
 include/grpc++/impl/codegen/status_code_enum.h \
 include/grpc++/impl/codegen/status_helper.h \
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index bca5652a..01b563d 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -822,6 +822,7 @@
 include/grpc++/impl/codegen/server_context.h \
 include/grpc++/impl/codegen/server_interface.h \
 include/grpc++/impl/codegen/service_type.h \
+include/grpc++/impl/codegen/slice.h \
 include/grpc++/impl/codegen/status.h \
 include/grpc++/impl/codegen/status_code_enum.h \
 include/grpc++/impl/codegen/status_helper.h \