Support more configurability in GN toolchains

tools/gn/example/hello_static.h

Index: tools/gn/example/hello_static.h
diff --git a/mojo/examples/echo/echo_service.mojom b/tools/gn/example/hello_static.h
similarity index 61%
copy from mojo/examples/echo/echo_service.mojom
copy to tools/gn/example/hello_static.h
index 6168d6ff2298185fb33e416e9f2eb76d952622fe..248ca0505d6fb2e5d5dbe2ecbf10cc28dcf24408 100644
--- a/mojo/examples/echo/echo_service.mojom
+++ b/tools/gn/example/hello_static.h
@@ -2,10 +2,9 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-module mojo.examples {
+#ifndef HELLO_STATIC_H_
+#define HELLO_STATIC_H_
 
-interface EchoService {
-  EchoString(string value) => (string value);
-};
+const char* GetStaticText();
 
-}
+#endif  // HELLO_STATIC_H_