Add initial prototype for the GN meta-buildsystem.

tools/gn/ninja_build_writer.h

Index: tools/gn/ninja_build_writer.h
diff --git a/tools/gn/ninja_build_writer.h b/tools/gn/ninja_build_writer.h
new file mode 100644
index 0000000000000000000000000000000000000000..85548df769738f995a4b8b5aa0cee7628cbd794c
--- /dev/null
+++ b/tools/gn/ninja_build_writer.h
@@ -0,0 +1,53 @@
+// Copyright (c) 2013 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_NINJA_BUILD_WRITER_H_
+#define TOOLS_GN_NINJA_BUILD_WRITER_H_
+
+#include <iosfwd>
+#include <vector>
+
+#include "tools/gn/ninja_helper.h"
+#include "tools/gn/path_output.h"
+
+class BuildSettings;
+class Settings;
+class Target;
+
+// Generates the toplevel "build.ninja" file. This references the individual
+// toolchain files and lists all input .gn files as dependencies of the
+// build itself.
+class NinjaBuildWriter {
+ public:
+  static bool RunAndWriteFile(
+      const BuildSettings* settings,
+      const std::vector<const Settings*>& all_settings,
+      const std::vector<const Target*>& default_toolchain_targets);
+
+ private:
+  NinjaBuildWriter(const BuildSettings* settings,
+                   const std::vector<const Settings*>& all_settings,
+                   const std::vector<const Target*>& default_toolchain_targets,
+                   std::ostream& out);
+  ~NinjaBuildWriter();
+
+  void Run();
+
+  void WriteNinjaRules();
+  void WriteSubninjas();
+  void WritePhonyAndAllRules();
+
+  const BuildSettings* build_settings_;
+  std::vector<const Settings*> all_settings_;
+  std::vector<const Target*> default_toolchain_targets_;
+  std::ostream& out_;
+  PathOutput path_output_;
+
+  NinjaHelper helper_;
+
+  DISALLOW_COPY_AND_ASSIGN(NinjaBuildWriter);
+};
+
+#endif  // TOOLS_GN_NINJA_BUILD_GENERATOR_H_
+