[GN] Add JSON project writer

tools/gn/json_project_writer.h

Index: tools/gn/json_project_writer.h
diff --git a/tools/gn/json_project_writer.h b/tools/gn/json_project_writer.h
new file mode 100644
index 0000000000000000000000000000000000000000..a4dbb66d572e3ec1283e9bfa8f5bbaff10918449
--- /dev/null
+++ b/tools/gn/json_project_writer.h
@@ -0,0 +1,25 @@
+// 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 std::string & file_name,
+                               const std::string & exec_script,
+                               const std::string & exec_script_extra_args,
+                               bool quiet,
+                               Err* err);
+};
+
+#endif