Add ninja dependency 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 45387a3967555394005d7455117160379055f25c..767bee78fa238e39d4a99be2551b59f6bb3de42e 100644
--- a/tools/gn/function_write_file.cc
+++ b/tools/gn/function_write_file.cc
@@ -114,6 +114,11 @@ Value RunWriteFile(Scope* scope,
           source_file.value(), args[0].origin(), err))
     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.
+  g_scheduler->AddGenDependency(
+      scope->settings()->build_settings()->GetFullPath(source_file));
 
   // Compute output.
   std::ostringstream contents;