Add output reference to gen written files.

tools/gn/function_write_file.cc

Index: tools/gn/function_write_file.cc
diff --git a/tools/gn/function_write_file.cc b/tools/gn/function_write_file.cc
index d24abc159ac5270046cf7a915b9bac70edea0163..45387a3967555394005d7455117160379055f25c 100644
--- a/tools/gn/function_write_file.cc
+++ b/tools/gn/function_write_file.cc
@@ -115,14 +115,6 @@ Value RunWriteFile(Scope* scope,
     return Value();
   g_scheduler->AddWrittenFile(source_file);  // Track that we wrote this file.
 
-  // Track how to recreate this file, since we write it a gen time.
-  // Note this is a hack since the correct output is not a dependency proper,
-  // but an addition of this file to the output of the gn rule that writes it.
-  // This dependency will, however, cause the gen step to be re-run and the
-  // build restarted if the file is missing.
-  g_scheduler->AddGenDependency(
-      scope->settings()->build_settings()->GetFullPath(source_file));
-
   // Compute output.
   std::ostringstream contents;
   if (args[1].type() == Value::LIST) {