Add a sanity check for inclusion of port_platform.h
diff --git a/src/core/ext/filters/deadline/deadline_filter.cc b/src/core/ext/filters/deadline/deadline_filter.cc
index 76c1204..dda3b61 100644
--- a/src/core/ext/filters/deadline/deadline_filter.cc
+++ b/src/core/ext/filters/deadline/deadline_filter.cc
@@ -14,6 +14,8 @@
 // limitations under the License.
 //
 
+#include <grpc/support/port_platform.h>
+
 #include "src/core/ext/filters/deadline/deadline_filter.h"
 
 #include <stdbool.h>