Implement call combiner.
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index 67dfb06..753bbac 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -944,6 +944,7 @@
 src/core/lib/http/format_request.h \
 src/core/lib/http/httpcli.h \
 src/core/lib/http/parser.h \
+src/core/lib/iomgr/call_combiner.h \
 src/core/lib/iomgr/closure.h \
 src/core/lib/iomgr/combiner.h \
 src/core/lib/iomgr/endpoint.h \