Add sync_custom.h
diff --git a/BUILD b/BUILD
index d10c9fd..8c10f11 100644
--- a/BUILD
+++ b/BUILD
@@ -57,6 +57,7 @@
     "include/grpc/support/string_util.h",
     "include/grpc/support/subprocess.h",
     "include/grpc/support/sync.h",
+    "include/grpc/support/sync_custom.h",
     "include/grpc/support/sync_generic.h",
     "include/grpc/support/sync_posix.h",
     "include/grpc/support/sync_windows.h",
@@ -545,6 +546,7 @@
         "include/grpc/impl/codegen/gpr_types.h",
         "include/grpc/impl/codegen/port_platform.h",
         "include/grpc/impl/codegen/sync.h",
+        "include/grpc/impl/codegen/sync_custom.h",
         "include/grpc/impl/codegen/sync_generic.h",
         "include/grpc/impl/codegen/sync_posix.h",
         "include/grpc/impl/codegen/sync_windows.h",