Activate FuzzDDLThreading

This was landed but not turned on. D'oh!

Bug: skia:10286
Change-Id: I65682370046c87c854d806253db32795ef3a9d14
Cq-Include-Trybots: luci.skia.skia.primary:Fuzz-Debian10-Clang
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/375736
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Adlai Holler <adlai@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 497af01..1bdc96e 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2950,6 +2950,14 @@
       deps = []
     }
 
+    libfuzzer_app("api_ddl_threading") {
+      sources = [
+        "fuzz/FuzzDDLThreading.cpp",
+        "fuzz/oss_fuzz/FuzzDDLThreading.cpp",
+      ]
+      deps = []
+    }
+
     libfuzzer_app("api_gradients") {
       sources = [
         "fuzz/FuzzGradients.cpp",