GN: don't write separate files for non-binary targets

tools/gn/json_project_writer.h

 // Copyright (c) 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef TOOLS_GN_JSON_WRITER_H_
 #define TOOLS_GN_JSON_WRITER_H_
 
 #include "tools/gn/err.h"
 #include "tools/gn/target.h"
 
 class Builder;
 class BuildSettings;
 
 class JSONProjectWriter {
  public:
   static bool RunAndWriteFiles(const BuildSettings* build_setting,
-                               const Builder* builder,
+                               const Builder& builder,
                                const std::string& file_name,
                                const std::string& exec_script,
                                const std::string& exec_script_extra_args,
                                const std::string& dir_filter_string,
                                bool quiet,
                                Err* err);
 };
 
 #endif