Add service_test GN template

services/catalog/public/tools/catalog.gni

Index: services/catalog/public/tools/catalog.gni
diff --git a/services/catalog/public/tools/catalog.gni b/services/catalog/public/tools/catalog.gni
index ae112b4ad4f13857d5ff4a0ad7d7c088769ee3ac..67a5774442866e9b2c07fce063e768d2d7ba6940 100644
--- a/services/catalog/public/tools/catalog.gni
+++ b/services/catalog/public/tools/catalog.gni
@@ -138,3 +138,58 @@ template("catalog") {
     }
   }
 }
+
+# Generates a source_set target which defines a single string contstant
+# containing the contents of a compiled catalog manifest.
+#
+# Parameters:
+#
+#   catalog
+#       The catalog target whose output should be stringified.
+#
+#   output_symbol_name
+#       The fully qualified symbol name of the C++ string constant to define in
+#       the generate source_set.
+#
+template("catalog_cpp_source") {
+  assert(defined(invoker.catalog), "catalog is required")
+  assert(defined(invoker.output_symbol_name), "output_symbol_name is required")
+
+  catalog_target = invoker.catalog
+  catalog_target_dir = get_label_info(catalog_target, "target_gen_dir")
+  catalog_target_name = get_label_info(catalog_target, "name")
+  catalog_filename = "$catalog_target_dir/${catalog_target_name}.json"
+
+  generator_target_name = "${target_name}__generator"
+  generated_filename = "${target_gen_dir}/${target_name}.cc"
+
+  action(generator_target_name) {
+    testonly = defined(invoker.testonly) && invoker.testonly
+    script = "//services/catalog/public/tools/sourcify_manifest.py"
+    inputs = [
+      catalog_filename,
+    ]
+    outputs = [
+      generated_filename,
+    ]
+    args = [
+      "--input=" + rebase_path(catalog_filename, root_build_dir),
+      "--output=" + rebase_path(generated_filename, root_build_dir),
+      "--symbol-name=" + invoker.output_symbol_name,
+    ]
+    if (is_debug || dcheck_always_on) {
+      args += [ "--pretty" ]
+    }
+    deps = [
+      catalog_target,
+    ]
+  }
+
+  source_set(target_name) {
+    testonly = defined(invoker.testonly) && invoker.testonly
+    sources = get_target_outputs(":$generator_target_name")
+    deps = [
+      ":$generator_target_name",
+    ]
+  }
+}