gn: make gn gen preserve import statements passed in --args

tools/gn/command_format.h

+// Copyright 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_COMAND_FORMAT_H_
+#define TOOLS_GN_COMAND_FORMAT_H_
+
+#include <string>
+
+class Setup;
+class SourceFile;
+
+namespace commands {
+
+bool FormatFileToString(Setup* setup,
+                        const SourceFile& file,
+                        bool dump_tree,
+                        std::string* output);
+
+bool FormatStringToString(const std::string& input,
+                          bool dump_tree,
+                          std::string* output);
+
+}  // namespace commands
+
+#endif  // TOOLS_GN_COMAND_FORMAT_H_
+